evaluation of botanical pesticides and coloured sticky

EVALUATION OF BOTANICAL PESTICIDES AND COLOURED STICKY INSECT

TRAPS FOR MANAGEMENT OF INSECT PESTS (THRIPS, WHITEFLIES AND

APHIDS) IN FRENCH BEANS (PHASEOLUS VULGARIS L.)

FAITH NJERI MWANGI

B. Sc. AGRICULTURE (UNIVERSITY OF NAIROBI)

A Thesis Submitted In Partial Fulfillment for the Requirement for the Award of Master of

Science Degree in Crop Protection of the University of Nairobi, Department of Plant

Science and Crop Protection

2015

DECLARATION

I declare that this is my original work and has not been presented for award of a degree in any

other University.

Signed………………………………………………..Date……………………………..

Faith Njeri Mwangi

Supervisors

This thesis has been submitted with our approval as university supervisors:

Signed…………………………………………………Date……………………………….

Dr Dora Kilalo PhD

Department of Plant Science and Crop Protection

University of Nairobi

Signed…………………………………………………Date……………………………….

Prof Florence Olubayo PhD

Department of Plant Science and Crop Protection

University of Nairobi

iii

UNIVERSITY OF NAIROBI

Declaration of Originality Form

Name of Student: Faith Njeri Mwangi

Registration Number: A56/71542/2011

College: College of Agriculture and Veterinary Sciences

Faculty/School/Institute: Faculty of Agriculture

Department: Department of Plant Science and Crop Protection

Course Name: Master of Science Degree in Crop Protection

Title of the work: Evaluation of botanical pesticides and coloured sticky insect traps for

management of insect pests (thrips, whiteflies and aphids) in French beans (Phaseolus vulgaris

L.)

DECLARATION

i. I understand what Plagiarism is and I am aware of the University’s Policy in this regard

ii. I declare that this Thesis is my original work and has not been submitted elsewhere for

examination, award of a degree or publication. Where other people’s work or my own

work has been used, this has properly been acknowledged and referenced in accordance

with the University of Nairobi’s requirements.

iii. I have not sought or used the services of any professional agencies to produce this work

iv. I have not allowed, and shall not allow anyone to copy my work with the intention of

passing it off as his/her own work.

v. I understand that any false claim in respect of this work shall result in disciplinary action,

in accordance with University Plagiarism Policy.

Signature ……………………

Date ………………………..

iv

DEDICATION

I dedicate this work to my family particularly my husband, my children and the entire extended

family who gave me unwavering support throughout my study. May the Lord God Almighty

bless them and guide them in all their endeavours.

v

ACKNOWLEDGEMENT

The success of this work is a joint effort of all the people and institutions which played key roles

in this study. I am grateful to the Ministry of Agriculture for a two-year sponsorship of my

studies as well as granting me study leave, particularly Mrs Ann Kiruri who encouraged me to

pursue the course in crop protection. I take this opportunity to thank all my supervisors; Dr.Dora

Kilalo for her constructive comments and useful advice greatly guided me in writing the thesis

throughout the study and Prof. Florence Olubayo for the support and encouragement she gave

me during the study.

I acknowledge the members of staff in the Department of Plant Science and Plant Protection

particularly the entire teaching staff and the technicians Mr. J. Aura, Mr. J. Wagura and Mr. G.

Anyika for the support they accorded me when I spent many hours in the laboratory. I cannot

forget the casual workers who assisted me in weeding, spraying, irrigating and harvesting. I

would also like to thank my fellow students particularly, Miss. F. Kirira and Mrs. E. Kihoro who

kept on encouraging me to continue writing. Finally, I want to thank my family members,

relatives and friends for their prayers, encouragement and moral support throughout my study.

vi

TABLE OF CONTENT

DECLARATION........................................................................................................................... ii

Declaration of Originality Form ................................................................................................. iii

DEDICATION.............................................................................................................................. iv

ACKNOWLEDGEMENT ............................................................................................................ v

TABLE OF CONTENT ............................................................................................................... vi

ABSTRACT ................................................................................................................................ xiii

CHAPTER ONE ........................................................................................................................... 1

INTRODUCTION......................................................................................................................... 1

1.1 Production and consumption of French beans ...................................................................... 1

1.2 Importance of French beans in horticultural industry ........................................................... 2

1.3 Problem statement ................................................................................................................. 3

1.4 Justification of the study ....................................................................................................... 4

1.5 Objectives ............................................................................................................................. 5

1.5.1 Overall Objective ............................................................................................................5

1.5.2 Specific Objectives ....................................................................................................5

1.6 Hypotheses ............................................................................................................................ 5

CHAPTER TWO .......................................................................................................................... 6

LITERATURE REVIEW ............................................................................................................ 6

2.1. French bean production and constraints in Kenya ............................................................... 6

2.2 Insect pests and diseases of French beans............................................................................. 8

2.2.1.1 Frankliniella occidentalis Pergande ............................................................................9

2.2.1.2. Frankliniella schultzei Trybom...................................................................................9

2.2.1.3. Megalurothrips sjostedti Trybom .............................................................................10

2.2.2 Whiteflies (Bemisia tabaci) ..........................................................................................11

2.2.3 Aphids (Aphis fabae) ....................................................................................................12

2.3. Pest management Methods ................................................................................................ 13

2.3.2 Biological control..........................................................................................................14

2.3.3 Use of Traps in pest control ..........................................................................................15

2.3.4 Chemical methods .........................................................................................................17

2.4 Tephrosia vogelii Hook. f. (Papilionaceae, Fabaceae) ....................................................20

CHAPTER THREE .................................................................................................................... 27

vii

EFFECT OF BOTANICAL PESTICIDES ON FRENCH BEAN INSECT PESTS

(APHIDS, THRIPS AND WHITEFLIES) ................................................................................ 27

3.1 Abstract ............................................................................................................................... 27

3.2 INTRODUCTION .............................................................................................................. 28

3.2.1 Pest management in French beans ................................................................................28

3.3 Materials and methods ........................................................................................................ 30

3.3.1. Experimental site .........................................................................................................30

3.3.2 Crop establishment........................................................................................................30

3.3.3 Preparation of extracts, decis and nimbecidine .............................................................31

3.4 RESULTS ........................................................................................................................... 34

3.4.1. Effect of botanicals on aphids population in planting one ( Nov 2012 –Feb 2013) ....34

3.4.2 Effect of botanicals on thrips population in planting one (Nov 2012-Feb 2013) .........34

3.4.3 Effect of botanicals on whiteflies population in planting one (Nov 2012-Feb 2013) ..35

3.4.4. Effect of botanicals on aphids population in planting two (March-June 2013) ...........36

3.4.5 Effect of botanicals on thrips population in planting two ( March –June 2013) .........37

3.4.6 Effect of botanicals on whiteflies population in planting two ( March –June 2013) ...37

3.4.7 Effect of botanicals on aphids population in planting three ( April - July 2013) .........38

3.4.8 Effect of botanicals on thrips population in planting three ( April - July 2013) ...........39

3.4.9 Effect of botanicals on whiteflies population in planting three ( April - July 2012) ....39

3.4.10 Yield of French beans in planting one ........................................................................40

3.4. 11 Yield of French beans in planting two ......................................................................41

3.4.12 Yield of French beans in planting three .....................................................................41

3.5 Discussion ........................................................................................................................... 42

CHAPTER FOUR ....................................................................................................................... 46

EFFECT OF COLOURED STICKY TRAPS IN MANAGEMENT OF FLOWER THRIPS,

WHITEFLIES AND APHIDS AFFECTING FRENCH BEANS .......................................... 46

4.1 Abstract ............................................................................................................................... 46

4.2 INTRODUCTION .............................................................................................................. 47

4.3 MATERIALS AND METHODS ........................................................................................ 52

4.3.1 The Experimental site ...................................................................................................52

4.3.2 Experimental layout ......................................................................................................52

4.3.3 Data collection and analysis..........................................................................................54

4.4 RESULTS ........................................................................................................................... 55

4.4.1 Effect of coloured traps on aphids in planting one (Nov. 2012- Feb 2013) ................55

4.4.2 Effect of coloured traps on thrips on planting one (Nov. 2012- Feb 2013) ................56

viii

4.4.3 Effect of coloured traps on whiteflies in planting one (Nov. 2012- Feb 2013) ...........56

4.4.4 Effect of coloured traps on aphids in planting two (March 2013- June 2013) .............57

4.4.5 Effect of coloured traps on thrips in planting two (March 2013- June 2013) ..............58

4.4.6 Effect of colured traps on whiteflies in planting two (March 2013- June 2013) ..........58

4.4.7 Effect of coloured traps on aphids in planting three (April 2013- July 2013) ..............59

4.4.8 Effect of coloured traps on thrips in planting three (April 2013- July 2013) ...............60

4.4.9 Effects of coloured traps on whiteflies in planting three (April 2013- July 2013 ) ......60

4.4.10 Yield of French beans in planting one ........................................................................61

4.4.11 Yield of French beans in planting two ........................................................................62

4.4.12 Yield of French beans in planting three ......................................................................63

4.5 Discussion ........................................................................................................................... 64

CHAPTER 5 ................................................................................................................................ 67

GENERAL DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS .................... 67

5.1 General discussion .............................................................................................................. 67

5.2 Conclusions ......................................................................................................................... 68

5.3 Recommendations ............................................................................................................... 68

REFERENCES ............................................................................................................................ 70

ix

LIST OF TABLES

1.1 Production of French beans in Kenya…………………………………………………………3

3.1 Mean number of aphids recorded on French in planting one……………………….….….…34

3.2 Mean number of thrips recorded on French in planting one………………………………....35

3.3 Mean number of whiteflies recorded on French in planting one………………………….…36

3.4 Mean number of aphids recorded on French in planting two………………………………..36

3.5 Mean number of thrips recorded on French in planting two…………………………...……37

3.6 Mean number of whiteflies recorded on French in planting two…………………………….38

3.7 Mean number of aphids recorded on French in planting three………………………………38

3.8 Mean number of thrips recorded on French in planting three…………………………….…39

3.9 Mean number of whiteflies recorded on French in planting three………………………..….40

4.1 Mean number of aphids recorded on French bean in planting one…………………………..55

4.2 Mean number of thrips recorded on French bean in planting one………………………...…56

4.3 Mean number of whiteflies recorded on French bean in planting one……........................…57

4.4 Mean number of aphids recorded on French beans in planting two…………………………57

4.5 Mean number of thrips recorded on French beans in planting two………………………….58

4.6 Mean number of whiteflies recorded on French bean in planting two ……………..………59

4.7 Mean number of aphids recorded on French bean in planting three…………………...……59

4.8 Mean number of thrips recorded on French bean in planting three………………………....60

4.9 Mean number of whiteflies recorded on French beans in planting three…………………….61

x

LIST OF FIGURES

3.1 Layout of the treatments in the field………………………………………………………....30

3.2 Yield of French beans in planting one……………………………………………………....40

3.3 Yield of French beans in planting two……………………………………….………………41

3.4 Yield of French beans in planting three…………………………………………..…………42

4.1 Layout of the treatments in the field…………………………………………………………52

4.2 Yield of French beans in planting one……………………………………………………….62

4.3 Yield of French beans in planting two………………………………………………………63

4.4 Yield of French beans in planting three…………………………………………………...…64

xi

LIST OF PLATES

2.1 Western flower thrips (Frankliniella occidentalis)……………………………..……………..9

2.2 Common blossom thrip (Frankliniella schultzei)…………………………………………....10

2.3 African bean flower thrips (Megalurothrips sjostedti)……………………………..........…..11

2.4 White flies (Bemisia tabaci)…………………………………………………..……………..12

2.5 Black bean aphid (Aphis fabae)…………………………………………………………..….13

2.6 Tephrosia vogelii…………………………………………….…………………………........22

2.7 Tithonia diversifolia………………………………………………………………………….23

2.8 Tagetes minuta……………………………………………………….………………………24

2.9 Gynadropsis gynandra………………………………………………………………….……26

3.1 Plot of French beans after the second weeding……………………………………………....32

3.2 Plot of French beans with pods……………………………………………………………....33

4.1 Plot of French beans with colored traps………………………………………………...……53

4.2 Mounted colored yellow trap………………………………………………………………...53

4.3 Blue colored trap with pests stuck on it……………………………………………...............54

xii

ABBREVIATIONS AND ACRONYMS

CAN Calcium Ammonium Nitrate

CIAT Centro Internacional de Agricultura Tropical

CTDT Community Technology Development Trust

DAP Diammonium phosphate

HCDA Horticultural Crops Development Authority

ICIPE International Centre of Insect Physiology and Ecology.

SNV Netherlands Development Organization

RCBD Randomized Complete Block Design

WFT Western flower thrips

xiii

ABSTRACT

EVALUATION OF BOTANICAL PESTICIDES AND COLOURED STICKY INSECT

TRAPS FOR THE MANAGEMENT OF INSECT PESTS (THRIPS, WHITEFLIES AND

APHIDS) IN FRENCH BEANS (PHASEOLUS VULGARIS L.)

French bean, Phaseolus vulgaris L. is an important crop in Kenya mainly grown by small holder

farmers in various parts of the country. However, farmers face many challenges among them

pests and diseases.

The objective of the study was to evaluate the effectiveness of the botanical pesticides Tithonia

(Tithonia diversifolia), Tephrosia (Tephrosia vogelii), Tagetes (Tagetes minuta) and Spider plant

(Gynandropsis gynandra) extracts were used and coloured sticky traps, blue, yellow and clear to

control insect pests of French bean: thrips (Megalurothrips sjostedti Trybom, Frankliniella

occidentalis Pergade, Frankliniella schultzei Trybom, bean aphid (Aphis fabae Scopoli)) and

whiteflies (Bemisia tabaci). The experiment was laid out in a randomized complete block design

(RCBD) replicated three times. The treatment application was done once a week to control

thrips, whiteflies and aphids and the experiments were carried out in relay for three crop cycles.

The botanical pesticides were prepared from dried powdered leaves of Tithonia, Tephrosia,

Tagetes and Spider plant which were infused in hot water for twelve hours and then sieved using

muslin cloth. The extracts were sprayed on the French beans on a weekly basis. All the plant

extracts were compared with a synthetic pyrethroid (Decis) and a commercial pesticide derived

from neem product (Nimbecidine). In another experiment sticky colored traps blue, yellow and

clear were used for controlling aphids, thrips and whiteflies . The traps were mounted in the in

the middle of the plots 60 cm above the ground just before flowering. The traps were placed

xiv

weekly and assessment done for four weeks. The yields of French beans were recorded for each

planting.

Data was collected on a weekly basis where thrips population was assessed from 5 flowers per

plant on 5 plants randomly selected in the middle of each plot. The aphids and white flies were

assessed in the same manner but from 3 leaves and 3 plants.

All the plant extracts were effective in controlling the insect pests. Tephrosia was more effective

than the other extracts (p<0.05). However, there was no significant difference between by

Tephrosia and Tithonia treatments in reducing pest numbers. The two botanical pesticides

Tithonia (Tithonia diversifolia) and Tephrosia (Tephrosia vogelii) activity on aphids, thrips and

whiteflies was comparable to that of commercial pesticides (Decis and Nimbecidine) in reducing

pest population densities and damage caused by the target insect pests. The blue and yellow traps

were significantly (p<0.05) more effective than the clear traps in reducing target pests. The

chemical (Decis) treatment was superior and significantly different from the traps (p<0.05), as

was expected.

The study demonstrated that botanical pesticides and sticky colored traps have a role to play in

the management of insect pests (aphids, whiteflies and thrips) in French beans and can be used in

an integrated pest management strategy to reduce pesticide use in small scale farmers’ fields.

Botanical pesticides can be a sustainable alternative to synthetic pesticides for controlling pests

and diseases. Coloured sticky insect traps are usually used to monitor pests but can also be used

to mass trap insects and reduce the rate of increase of pests.

1

CHAPTER ONE

INTRODUCTION

1.1 Production and consumption of French beans

Snap bean (Phaseolus vulgaris L.), also widely known as French bean, is an important crop in

the socio-economic systems of East and Central Africa. It is a crop with great potential for

addressing food insecurity, improving incomes and alleviating poverty in the region (Kabata and

Anyango, 1996). It is grown in many areas of Kenya and its immature pods which are consumed

as fresh vegetables or processed and canned. The edible fresh pods contribute to human nutrition

by providing ascorbic acid, proteins, fibre, and minerals particularly iron, which is recommended

especially to expectant and lactating mothers (CIAT, 1988; Njeru, 1989).

The crop ranks highly among the export horticultural crops in Kenya. Other ECA countries with

increasing production of snap bean are Uganda, Tanzania and Rwanda. Snap bean production is

dominated by rural small-scale farmers (Wambua, 2004). The main challenges in snap

production include: (a) lack of high yielding, pest and disease resistance and premium market

value varieties; (b) high costs of pesticides; (c) low soil fertility and limited moisture; (d) high

post-harvest losses; and (e) market constraints including stringent requirements in the

international markets (Anon, 2000; Kasina, 2003; Monda et al., 2003).

French beans are a major export crop in Kenya whose local consumption is gradually being

adopted (Mishek, 2011). The crop is grown on small scale with staggered planting due to

intensive labour requirements. It is cultivated both for fresh consumption and processing either

canning or freezing.

2

The varieties of French beans which are grown in Kenya are determined by market preference

and these include Monel, Gloria, Claudia, Morgan, Amy coby, Espada, Maasai, Samantha,

Paulista, Slender green and Nerina. Farmers prefer high yielding varieties with straight long,

round and fleshy pods and with a long picking duration. With irrigation, all year round

production is possible but the main export planting is October to May and crop takes 45-50 days

from planting to first picking. (Farmers Pride International Company LTD – Mkulima online,

2014).

1.2 Importance of French beans in horticultural industry

French beans are grown in many areas of Kenya for the immature pods which are consumed as

fresh vegetables or processed and canned..The major French bean growing areas in Kenya are

Embu, Meru, Nyeri, Kirinyaga, Kiambu, Nairobi, Machakos, Makueni, Kericho, Nanyuki,

Muranga, Naivasha, Trans-Nzoia, Vihiga, Bungoma and Kericho. The production is done

throughout the year mainly under irrigation and it takes six to eight weeks from planting to

harvesting allowing quick returns on investment. The year round production of French beans is

hindered by accumulation of pests and diseases which are a major constraint. The range of pests

that attack French beans in order of importance are bean flies (Ophiomya spp), flower thrips

(Megalurothrips sjostedti Tribom and Frankliniella occidentalis Pergade), bean aphid (Aphis

fabae Scopoli), red spider mites (Tetranychus spp), African bollworm (Helicoverpa armigera

Hurbner), legume pod borer (Maruca testularis Geyer) and whiteflies, (Bemisia tabaci) (Lohr

and Michalik, 1995). The severity of the pests attack depends on location and planting (Seif, et

al., 2001).

3

About 80% of French beans in Kenya are produced by small scale farmers (Nderitu, et al., 2008).

They mainly grow French beans for the export as a source of income for the family. According

to SNV Netherlands Development Organization (2012), the sector employs 45,000 to 60,000

people. Sixty percent of the workers are women engaged in commercial farms and they dominate

post harvest handling of French beans; sorting, grading and in quality control. Farmers are

always under pressure to meet standards on product quality, food safety, traceability, occupation

health and safety of workers especially those set by the European Union which is the main

market for French beans from Kenya (Standard media July 29th 2014; Kenya Economic Survey

2013). Table 1.1 shows the production of French beans.

Table 1.1: Production of French beans in Kenya

Year Production (Ha) Production in (MT)

2007 7,733 67,330

2008 4,616 92,095

2009 3,336 46,496

2010

2012

4,840

4,128

55,841

44,000

Source:HCDA

1.3 Problem statement

Small holder farmers produce low yields of French beans mainly due to challenges of pests,

diseases and poor agronomic practices. Pests and diseases are mainly controlled using chemical

pesticides some of which have been detected as residues in farm produce during marketing.

Furthermore some of the chemicals used to control pests and diseases are pollutants of the

environment and are expensive. The chemical residues make the produce unmarketable hence

4

leading to loss of income for farmers. Resistance to the currently available synthetic insecticides

is another serious concern. For example, available information indicates that higher densities of

thrips especially Frankliniella occidentalis and Megalurothrips sjostedti were recorded in farms

with more frequent application of synthetic pyrethroids, indicating a high degree of resistance to

pyrethroids (ICIPE, 2011). There is need to evaluate other ways of managing pests and diseases

such as use of botanical pesticides and coloured sticky traps which can reduce the cost of

production, increase yields per unit area, enhance the family income and promote a clean

environment.

1.4 Justification of the study

French bean is an important crop for small holder farmers for income generation and

employment. Production constraints have been mainly bean pests, diseases and poor agronomical

practices. Residues in produce, pest resistance development and environmental pollution caused

by overuse of pesticides are matters of concern for both scientists and the consumers. There is

need to search for selective and biodegradable pesticides to solve problems of pests on farms and

long term toxicity to non-targeted insects, mammals and environment. Pesticides derived from

plant extracts can be alternatives to synthetic pesticides for controlling pests and diseases hence

can reduce negative impacts to human health and environment. The plant extracts are locally

available and can be a cheap alternative to the small holder farmers. Botanical pesticides may be

the key to organic, renewable and cost effective pest management strategy using readily

available materials. Similarly, colured traps for mass trapping may also be an alternative to

pesticide use.

5

The use of botanical pesticides and coloured sticky insect traps is another way of producing

French beans free of chemical residues. The results will contribute to the knowledge on clean

environment and safe production of crops in the country. Furthermore, the results will also

provide information for farmers and policy makers on integrated pest management other than use

of synthetic chemicals. This information will encourage the farmers to use readily available plant

materials and sticky traps in the control of pests to improve productivity of in Kenya.

1.5 Objectives

1.5.1 Overall Objective

The goal of this study was to improve French bean production by evaluating techniques that can

be used in an integrated pest management strategy for sustainable French bean production.

1.5.2 Specific Objectives

1. To determine the effect of botanicals, namely Tagetes (Tagetes minuta), Spider plant

(Gynandropsis gynandra), Tithonia (Tithonia diversifolia) and Tephrosia (Tephrosia

vogelii) water extracts, on flower thrips, whiteflies and aphids affecting French beans.

2. To assess the effect of different coloured sticky traps in the management of thrips,

whiteflies and aphids on French bean.

1.6 Hypotheses

i) Botanical pesticides can be used to control insect pests in French beans.

ii) Coloured sticky insect traps have no effect in reducing pest populations in French beans.

6

CHAPTER TWO

LITERATURE REVIEW

2.1. French bean production and constraints in Kenya

French beans (Phaseolus vulgaris) are known to grow from low lands of the warm tropics to the

cold high altitude mountains and hot desert. However, most common varieties grown in the

tropics perform well with relative narrow ecological zone ranging from 0-1000 m above sea level

(Tindall, 1983). In Kenya; French beans are known to grow well within the midland to lower

highland ecological zones. They perform better at an altitude between 1500 m and 2100 m above

sea level, at temperatures between 14-220C with moderate rainfall of 900-1200 mm. However,

most of the crop is grown under irrigation (Anon, 2000). French beans can grow in a wide range

of soils from sandy loam to clay but will grow best on friable, medium loam soils, well drained

and with a lot of organic matter (Anon, 2000). They need optimum pH levels of 6.5-7.5 but can

tolerate a low pH of 4.5-5.5 (Anon, 2000). The crop takes 45-50 days from planting to first

picking. Farm yard manure is recommended in poor soils at a rate of 10 tons/ha applied in

planting furrows. Two hundred kg per ha of DAP fertilizer is applied in the furrows and mixed

well before planting. At three leaf stage top dressing is carried out with 100 kg of CAN and a

second application follows at the onset of flowering. Foliar feed should be applied fortnightly

from the fourth week to mid podding stage (Kasina, 2003).

Excessive nitrogen promotes growth of leaves instead of pods. Regular watering is essential for

the promotion of high yields, uniformity and high quality. The crop is sensitive to water stress at

flowering.Waterlogging should also be avoided. Application of 35 mm of water per week at

planting to 10 days after germination and 50 mm thereafter to flowering stage is recommended

for good growth of French beans. Timely weed control is absolutely essential. The following pre-

7

emergence herbicides are recommended for French beans in Kenya (Farmers Pride International

Company LTD – Mkulima online, 2014). These are Lasso 4 EC( Alachlor)-3 litres in 400 litres

of water per hectare and Stomp (Pendimethalin)-2.5 Litres in 400 litres of water per hectare

Effective control of insect pests’ infestation can be achieved through use of conventional

insecticides. However, conventional pesticides are expensive; they result in ecological health

hazard and cause insect resurgence and can also lead to the development of resistance to the

pesticides and destruction of natural antagonists. Botanicals have been reported to have

insecticidal properties (Sohail, et al., 2012; Adebayo 2003; Adebayo and Gbolade, 1994).

Sustainable pest management is a prerequisite to farming in developing countries of Africa with

economic risks and uncertainties and harsh climatic conditions (Schwarb, et al., 1995). There is

renewed interest in the application of botanical pesticides for crop protection. Scientists have

continued to do research on indigenous plant materials which have positive activity in reducing

insect pests which attack crops (Roy, et al., 2005). Botanical pesticides are biodegradable

(Devlin and Zettel, 1999) and their use in crop protection is a practical sustainable alternative to

synthetic chemicals used to protect crops. They maintain biological diversity of predators and

reduce environmental contamination and human health hazards (Grange and Ahmed, 1988).

Research on active ingredients, pesticide preparations, application rates and environmental

impact of botanical pesticides are a prerequisite for sustainable agriculture (Buss and Park-

Brown 2002). Italo, et al., 2009, Jazzar and Hammand, 2003 have reported the insecticidal

effects of leaves and fruits of Melia azedarach L. on various insects.

Colored sticky traps that reflect certain wavelengths of yellow, blue, white and red are most

often used to attract and catch insect pests such as winged aphids, whiteflies, thrips, leafminers,

8

fungus gnats, and shoreflies eg. Scatella stagnalis (Fallen) Ephydridae, DIPTERA (Rodriguez-

Saona, et al., 2012; Taha, et al., 2012). Blue traps are said to be better at capturing western

flower thrips and shore flies. However, it is suggested that yellow traps be used in a monitoring

program that include whiteflies and fungus gnats. Traps can also be used to control some pests or

at least slow the rate of increase of pests such as whiteflies (Pasian and Lindquist, 2009).

2.2 Insect pests and diseases of French beans

Arthropod pests are the major constraints contributing to high yield loss, while high cost of

inputs (certified seeds, labour and fertilizers) make farmers produce in small areas ranging from

0.25 – 2 acres. Continuous production of the crop throughout the year coupled by poor pests

control strategies encourages pests and diseases build up (Makokha, et al., 2001). The crop is

attacked by a host of pests and diseases which include the bean fly (Ophiomya spp), flower thrips

(Megalurothrips sjostedti Trybom), (Frankliniella occidentalis Pergade), (Frankliniella schultzei

Trybom), bean aphid (Aphis fabae Scopoli), Red spider mites (Tetranychus spp), African boll

worm (Helicoverpa armigera Hurbner), Legume borer (Maruca testularis Geyer) and whiteflies

(Bemisia tabaci). Damage due to thrips is reported to be as high as 70% in French beans in

Kenya and Uganda (Lohr and Machalik, 1995, ICIPE, 2011).

2.2.1. Thrips

Thrips inhabit flowers, shoots and tender leaves (Tamo et al., 1993). They feed on flowers

causing abscission of flower buds and curling of pods that lead to low yields. The silvery lesions

made on the pods render the product unfit for export ( Kibata and Anyango, 1996).

9

2.2.1.1 Frankliniella occidentalis Pergande

Frankliniella occidentalis is known to be a native of Pacific states of North America (Kasina,

2003) and has spread to colonize almost the entire world. The pest is identified by the number of

setae on the pronotum, the number of pairs of setae between the compound eyes and ocelli, and

the presence of two complete rows of setae on the wings of Frankliniella spp (Plate 2.1).

Plate 2.1.Western flower thrips (Frankliniella occidentalis)

http:/nfrec.ifas.ufas.ufl.edu/programs/tomato_spotted_wilt_management.shtml

2.2.1.2. Frankliniella schultzei Trybom

Frankliniella schultzei Trybom is known as commom blossom thrip (plate. 2.2). It is found in the

tropics and sub- tropics (Viebergen and Mantel, 1991). In Australia, it was known as

Frankliniella lycopersici Steele. It is found in both the dark and pale forms; the dark form is

found in south Sudan to Cape Town while the pale form is found in Egypt, Sudan, Uganda and

Kenya (Mound, 2004; Sakimura, 1969).

10

Plate 2.2. Commom blossom thrip (Frankliniella schultzei) www.ozthrips.org/terebrantia/thripidae/thripinae/frankliniella schultzei/

2.2.1.3. Megalurothrips sjostedti Trybom

Megalurothrips sjostedti Trybom is from Africa, in the Ethiopian, Niger and the Cape regions

including the Cape Islands (Palmer, 1987). For many years, the pest was known as Taeniothrips

sjostedti until after Bhatti (1969) did a series of studies, which led to substantial changes of

generic relationships in the sub-family, Thripinae (Plate 2.3). The pest is found throughout Sub-

Sahara Africa where it has been documented in Ethiopia, Niger and Kenya, (Taylor, 1974; Tamo

et al.,1993; Kyamanywa et al., 1993a; Kyamanywa et al., 1993b and Mensah, 1988).

Megalurothrips sjostedti is considered an African thrip and has been reported as a pest in East

Africa (Faure, 1960). Megalurothrips sjostedti differs from Frankliniella spp. by having a

pronotum with one pair of long setae at the anterior margin while the latter has two pairs.

http://www.ozthrips.org/terebrantia/thripidae/thripinae/frankliniella%20schultzei/

11

Plate 2.3. African bean flower thrips (Megalurothrips sjostedti)

www.infonet-biovision.org/default/ct/120/crops

2.2.2 Whiteflies (Bemisia tabaci)

Whiteflies belong to the order Hemiptera; sub-order Homoptera and family Aleyrodidae (Fig

2.5). There are more than 1500 species. (Lohr and Michalik, 1995).They typically feed on the

underside of the plant leaves. The life cycle of whiteflies is given in Plate 2.4. The genus Bemisia

is important in transmission of crop diseases particularly the bean dwarf mosaic and bean golden

mosaic diseases. The severity of the pest infestation depends on location and planting (Seif et al.,

2001).

http://www.infonet-biovision.org/default/ct/120/crops

12

Plate 2.4. White flies (Bemisia tabaci)

http:/entnemdept.ufl.edu/creaturers/veg/leaf/silverleaf_whitefly.htm

2.2.3 Aphids (Aphis fabae)

Black bean aphid (Aphis fabae) belongs to the family Aphididae (Plate 2.5). It is a major pest of

legume which attacks early and can greatly affect the yields of the beans. Aphids are tiny and are

insects that suck sap from the plants. They develop rapidly in warm and dry weather and high

populations can build up quickly. A part from sucking plant sap, aphids transmit virus causing

plant diseases in many crops (Raccah and Ferere, 2009).

13

Plate 2.5. Black bean aphid (Aphis fabae)

www.agroatlas.ru/pests/Aphis fabae_en.htm

2.3. Pest management Methods

Major pest and diseases in growing of French beans includes fungal diseases, insect attacks and

nematodes. Control is mainly by application of recommended pesticides, crop rotation, and use

of certified seeds, field hygiene and crop rotation (Mishek, 2011; Nderitu, et al. 2001, 2007,

2008).

2.3.1. Cultural Practices

Cultural practice is the purposeful manipulation of the crop environment to reduce the rate of

pest increase and damage. Cultural practices are used to control thrips on legume crops in

various parts of the world. Intercropping of legumes such as cowpeas with groundnuts and other

crops is reported as one of the effective cultural methods for controlling thrips of legume crops

(Emeasor and Ezueh, 1977; Kyamanywa and Kuo, 1996). The timing of intercropping is very

important in thrips management. Intercropping cowpeas and maize crop significantly reduce the

http://www.agroatlas.ru/pests/Aphis

14

insect damage (Ezueh and Taylor, 1984). Flooding fields with irrigation has been used to destroy

a large proportion of pupal population stage of thrips in the soil (Pathak and Khan, 1994).

Pesticide Action Network (2005) has listed many cultural practices used to control pests in

French beans. These cultural practices include increasing seeding/seedling rate, mulching,

planting flowering grasses around field margins and planting tobacco as a trap. Pests that are

controlled include aphids, whiteflies, and bean flies; nematodes and diseases such as

anthracnose, bacterial leaf blight and rust. Natural enemies such as spider and ladybird beetles

can also control aphid and whiteflies populations. Other governments and organizations have

articulated the role of cultural practices in an integrated pest management (Queensland

Government, 2013; CTDT, 2008).

2.3.2 Biological control

Biological control is the use of living organisms to manipulate insect populations.The use of

inundative biological control in the protected growing conditions with the predatory mites

(Neoseiulus cumeris and Amblyseius barkeri) or predatory bugs (Orius species) is a routine

practice in Europe and the United States of America (Lenteren, 2012; Lenteren, 2003). In Kenya,

studies by Gitonga (1999) showed that a predator Orius species and a parastoid Ceranisus menes

had low predation and parasitism hence the need for augmentation. Example of entomo-

pathogenic fungi used in biological control methods include Beauveria spp, Trichoderma spp.,

and Metarhizium spp. Isolates of pathogenic fungi have been available for many years in Europe

for control of thrips and other glasshouse pests (Helyer, et al., 1995). A lot of research work has

also been carried out in Kenya especially at International Centre of Insect Physiology and

Ecology (ICIPE) on Beauveria spp, and Metarhizium spp. Omukoko, et al., (2011) found that

the ten isolates of Beauveria bassiana tested were pathogenic to adult banana weevil with isolate

15

ICIPE 273 and M313 being the most active. Ouna, (2010) and Ouna, et al., (2010) reported

that out of the 24 isolates of Metarhizium anisopliae and Beauveria bassiana screened for

pathogenicity against Bactrocera invadens (mango fruit fly), 7 isolates and M. anisopliae var.

acridium (ICIPE 21), induced significantly high mortalities. The results reported by Mburu, et

al., (2009) showed that termite’s response to Metarhizium anisopliae or Beauveria bassiana is

directly related to the potential harm these fungi can inflict on the insect and that the virulent

strains are more likely to be recognized from some distance and avoided. Karanja, et al., (2010)

reported that pathological entomopathogens Metarhizium anisopliae and Beauveria bassiana

were potential biological agents as the isolates of these fungi caused infection and death to white

coffee stem borer in Kenya.

2.3.3 Use of Traps in pest control

Concerns about the potentially negative impacts of broad spectrum insecticides on environmental

quality, food security and natural enemies have lead to research aimed at minimizing the use of

insecticides for pest management (Grzywacz, et al., 2014). Use of traps is one of the

interventions of pest pest management (Wallis and Shaw, 2008). Insect traps are useful tools for

monitoring insect populations to determine the need for control or the timing of control practices

(Covaci et al., 2012). In some instances, attractants and traps can be used together to control

insect populations directly by mass trapping or mating disruption (Thomson, et al., 2004). Mass

trapping is most likely to be effective when the density of the target pest is low and immigration

into the trapped area is minimal, as is the case in restricted environments (e.g. greenhouses)

(www.infonet.org). Insect traps consist of a visual (colour, shapes and light) and/or chemical

(scent/pheromone) attractant to attract the target insect, plus a device to capture the insect once it

arrives. Most insect traps either use glue to immobilize insects or have funnel structures to

http://www.infonet.org/

16

prevent them from escaping (Kasina, et al., 2009; Hoddle, et al., 2002). Traps are used for one of

the two reasons: One trapping and secondly monitoring of insect pests. Colored sticky traps, with

or without pheromones are often used to attract various insect pests depending on the colour.

Colours, including blue, yellow, white, red, green, pink and orange traps, are used to attract

different insect pests. Although some colored traps have minimal attraction on certain insect

pests, others may trap non-target/beneficial insects (Barrett, 1992; Clare, et al., 2000, Wallis and

Shaw 2008). Sticky yellow traps have been tested severally (Atakan and Canhilal, 2004).

According to Kaas (2005), insects are differentially attracted to coloured surfaces, particularly

yellow which is notorious among house painters as a general insect attractant. This feature has

been exploited among entomologists for collection of Coleoptera, Cicadellidae, aphids,

Hymenoptera and Thysanoptera (Kaas, 2005).

Literature indicates that different sticky coloured traps are used for different pests. Field

experiments conducted to determine the attractive action of different colors to Tuta absoluta

moths (Taha, et al., 2012) showed that the red sticky traps caught the greatest number of moths,

while the yellow sticky traps caught the fewest number of moths. Other field experiments

conducted to determine adult attraction of the blunt-nosed leafhopper, Limotettix vaccinii (Van

Duzee), and the sharp-nosed leafhopper, Scaphytopius magdalensis (Provancher), to colored

sticky traps indicated that green was the most attractive color to blunt-nosed leafhoppers,

followed by red and yellow; whereas yellow was the most attractive to sharp-nosed leafhoppers,

followed by green and red (Rodriguez-Saona et al., 2012). The response of Ceratothripoides

claratris, a pest on tomato, to colors was also evaluated in a pesticide free tomato field

(Ranamukhaarachchi and Wickramarachchi, 2007). Many colors were tested but blue and white

trapped more C. claratris compared to the rest. In another field study conducted to evaluate

http://cabdirect.org/search.html?q=au%3A%22Barrett%2C+B.+A.%22

http://www.sciencedirect.com/science/article/pii/S0261219412001330

17

various colour sticky traps and light traps in sugarcane fields for the insect vectors of sugarcane

white leaf phytoplasma, the leafhoppers Matsumuratettix hiroglyphicus (Matsumura) and

Yamatotettix flavovittatus (Thein et al., 2011), a higher number of the putative vectors,

Matsumuratettix hiroglyphicus and Yamatotettix flavovittatus were trapped on blue and yellow

than in other sticky traps. Hassan and Mohammed (2004) while evaluating the insects trapping

efficiency of various colored traps to monitor thrips Thrips tabaci (Lindeman) and the leafminer

Liriomyze trifolii (Burgess), they demonstrated that significantly higher mean number of insect

pests trapped on fluorescent yellow traps compared to other coloured traps.

2.3.4 Chemical methods

Chemical control is the use of chemical insecticides to kill, deter or influence pests for control

purposes. Use of conventional insecticides for pest management is the most frequently used

method to suppress insect pests of French beans in Kenya (Wambua, 2004; Pest Control

Products Board, 2014). Some of the commonly used insecticides to control thrips, aphids and

whiteflies include synthetic pyrethrins, carbamates, neonicotinoids and benzourea based

insecticides (Kasina, 2003; Misheck, 2011, Pest Control Products Board, 2014). In Kenya,

pesticides use for the control of thrips on French beans has been evaluated and recommendations

made (Kibata and Onyango, 1996, Muriuki, 1988, Wambua, 2004). The introduction of

maximum residue levels in export produce by the European Union posed and still poses a

challenge in the horticulture industry (Lohr, 1996). Although use of chemical pesticides is the

most common method of pest management, the chemicals are expensive for small scale farmers,

thereby increasing cost of production and reducing the farmers’ income (Mishek, 2011).

18

2.3.5 Use of botanical pesticides in insect pest control

Effective control of insect pests’ infestation can be achieved through use of conventional

insecticides. However, conventional pesticides are expensive, result in ecological pollution,

health hazards and cause pest resurgence by destroying the natural enemies (Isman, 2008).

Botanicals have been reported to have insecticidal properties but their efficacy in controlling

pests on various crops remains largely unknown. However, there are reports on some pesticidal

activities of some plants. Adebayo and Olaifa (2004) and Oparaeke, et al. (2005) investigated a

mixture of Neem and Eucalyptus leaf extracts with leaf extract of other plant species efficacy in the

management of two major post flowering insect pests (Maruca pod borers and Clavigralla

tomentosicollis Stal.) of cowpea. The extract mixtures caused great reduction in pod damage per

plant and ensured higher grain yield compared with the unsprayed plots (Oparaeke et al., 2005).

The complementary roles played by individual plant species used for the extracts mixtures in

reducing pests numbers and increasing grain yields on sprayed plots suggested the future direction of

new formulations of biopesticides in the management of field pests of crops on farms owned by

resource limited farmers in low input agriculture characterizing the developing countries (Oparaeke

et al., 2005). Sustainable pest management is a prerequisite to farming in developing countries of

Africa with economic risks and uncertainties and harsh climatic conditions. There is renewed

interest in the application of botanical pesticides for crop protection. Research on indigenous

plant materials to protect insect infestation on crops has been of interest to researchers (Roy et

al., 2005).

Botanical pesticides are biodegradable (Devlin and Zeltel, 1999) and their use in crop protection

is a practical sustainable alternative. They maintain biological diversity of predators and reduce

environmental contamination and human health hazards (Grange and Ahmed, 1988). Research

19

on active ingredients, pesticide preparations, application rates and environmental impact of

botanical pesticides are a prerequisite for sustainable agriculture (Buss and Park-Brown, 2002).

Evaluation of various botanical pesticides used in controlling insect pests has been done and has

shown reduced pest populations (Henn and Weinzierl, 1989). Use of botanicals is prefered in

organic food production, both in the field and in controlled environments (Isman, 2008). Recent

studies in Africa, suggest that extracts of locally available plants can be effective as crop

protectants, either used alone or in mixtures with conventional insecticides at reduced rates

(Kareru et al., 2013; Khater, 2012). The studies suggest that indigenous knowledge and

traditional practice can make valuable contributions to domestic food production. Further more,

botanical insecticides have long been considered as an attractive alternative to synthetic chemical

insecticides in pest management. This is because they pose little threat to environment and

humans. They are also suited for use in organic food production in industrialized countries and

they play a much greater role in crop production and post-harvest management of food in

developing coutries (Isman, 2006 and 2008).

Generally botanical extracts act quickly, degrade rapidly and with few exceptions have low

mammalian toxicity. The most recent US Environmental Protection Agency Registration

Standard considered rotenone, the active ingredient of tephrosia to be non toxic by inhalation

rather than by ingestion (Neal,2013). However, standardization of some of these pesticides has

been commercialized for insect control for example azadirachtin (Henn and Weinzierl, 1989).

Azadirachtin is used as an insecticide and fungicide. It acts as a repellent, anti-feedant and

growth regulator (Henn and Weinzier, 1989). Tephrosia vogelii Hook. f.) Tithonia diversifolia

20

(Hemsl.) Gray, Tagetes minuta L. and Gynandropsis gynandra (L.) Brig. are some of the plants

which have been used by small scale farmers for pest control in French beans production.

2.4 Tephrosia vogelii Hook. f. (Papilionaceae, Fabaceae)

This is a woody perennial with leaflets 13-29 and bluish-green in colour (Plate 2.6). The veins

are prominent with silver hairs: flowers white or pale yellow in dense, terminal, shortly stalked

psedo-racemes; standard white-silky, about 22 mm long; pod 13 x1.5 mm, densely golden-hairy.

It is distributed in many parts of Kenya in waste grounds and well known as fish poison by the

indigenous people (Agnew and Agnew, 1994). Tephrosia vogelii has been extensively used as a

natural control of pests on snap beans, cowpea and pigeon peas among others (Adebayo and

Olaifa, 2004). In a study to evaluate the effectiveness of botanical pesticides for the control of

insect pests in cowpea, T. vogelii was the most active and was ranked equal to the synthetic

Decis in reducing the population density and damage (Adebayo et al., 2007). Lao et al., (2011)

evaluated the natural toxicant from Tephrosia vogelii and Petiveria alliacea and their mixture

against Megalurothrips sjostedti and Apion varium on cowpeas. The findings showed that the

two insect pests were effectively controlled by the botanical insecticides compared to the

untreated plants. Tephrosia vogelii is toxic to insects and has repellent effects on maize weevils

(Ogendo, et al., 2003, 2004). It is effective against Macrotermes bellicosus, an emerging pest of

Cocoa (Oyedokum et al., 2011). In another recent experiment by Mudzingua et al.,

(2013) three plants, T. vogelii, Allium sativum and Solanum incanum were tested against aphids

(Brevicoryne brassicae L.) in rape seed (Brassica napus L.). Tephrosia vogelii extract was the

second most active after dimethoate (Mudzingua et al., 2013).

The efficacy of T. vogelii on insects feeding on pigeon pea in Kenya has been assessed. In one

such experiment, different concentrations of leaf water extracts were sprayed to the pigeon peas.

21

Tephrosia extract like dimethoate showed significant reduction in seed damage compared to the

control treatment. It was suggested that farmers be encouraged to grow the plant for easy

accessibility of the leaves (Minja, et al., 2002). According to Njiru, (2006) a combination of

rotenone, one of the major ingredients of T. vogelii, with pyrethrins is a safe insecticidal

formulation to human and environment. Tephrosia vogelii water extract has also been tested for

its activity against several termites, aphids and red spider mites with 20% w/v giving mortality of

more than 90% to the pests (McDavid and Lesseps, 1995). In another experiment, the results

indicated that T. vogelii in hexane extract and its mixture with Piper cubeba extract had potential

as an alternative to conventional insecticides for the control of crucifer pests (Nugroho, et al.,

2009). T. vogelii extract has also has been considered as a biorational insecticide by Namungu,

(2003). These are insecticides which are active against pest populations, but relatively innocuous

to non-target organisms and therefore, non-disruptive to biological control. An insecticide can be

“innocuous” by having low or no direct toxicity, or by having systemic or rapid translaminar

activity or short field residual, thereby minimizing exposure of natural enemies to the insecticide

(Schuster and Stansly, 2012).

The major ingredients in T. vogelii are rotenone, dequelin, alpha-toxicarol, tephrosin, sarcolobin

and 5-methoxyisolonchocarpin which are responsible for the insecticidal and antifeedant activity

(Carlson and Tallent, 1970; Belmain, et al., 2012; Wanga, 2003). Although these compounds are

highly toxic to numerous insects, Tephrosia extract is relatively non toxic to most mammals with

short residual time (Adebayo and Olaifa, 2007; Fukami et al., 1970; Barnes and Freyre, 1966).

The biocidal effect of fresh water extract is said to be more effective in the presence of soap

(Bandason and Mchingula, 2013).

22

Plate 2.6. Tephrosia vogelii

Source: FN Mwangi 2012

2.5. Tithonia diversifolia (Hemsl.) Gray (Compositae, Asteraceae)

This is a common plant introduced from Central America (Plate 2.7). The plant is used as a

hedge plant in Kenya. It is a soft shrub with simple to 3-lobed mostly opposite leaves; heads

large, orange yellow on an expanded stalk (Agnew and Agnew, 1994).

The powder and ethanol extract of Tithonia diversifolia leaves have been tested for their efficacy

mortality, oviposition and adult emergence of cowpea seed bruchid, (Callosobruchus

maculatus). The results indicated that T. diversifolia could be a potential candidate for bio-

insecticide preparations because of anti-ovipositional, ovicidal and knockdown properties of its

products (Adedire and Akinneye, 2004). The nematicidal effect of T. diversifolia among other

23

plants has been tested against Meloidogyne incognita and its extract has been shown to be as

effective as the nematicide carbofuran in management of root-knot nematode (Akpheokhai,et al.,

2012). Moreno (1991) studied the possible utilization of wild sunflower (Tithonia diversifolia A.

Gray) leaf extract as an insecticide against selected vegetable insect pests. The water extract of

Tithonia diversifolia was found to be the best for control of Periplanata americana over organic

extracts (Ambama, 2013). Toxicity studies demonstrate that it can be considered as a safe,

biodegradable and renewable source of the botanical pesticide (Maud, et al., 2011).

Plate. 2. 7. Tithonia diversifolia


2.6 Tagetes minuta L. (Compositae, Asteraceae)

This is an erect strong-smelling annual, often very robust but variable in habit; the leaves are

pinnate with elliptic toothed leaflets, heads creamy yellow, in terminal corymbs; phyllaries 10

cm long (Plate 2.8). The plant is abundant and a troublesome weed in upland arable land and

was introduced from America. It is widely distributed in many parts of Kenya (Agnew and

24

Agnew, 1994). Tagetes has been used as a pesticide especially in repelling insects traditionally

(Opender, et al., 2008). Tagetes has also been used as an intercrop with vegetable crops like

onions to control pests (Waiganjo, et al., 2007). A patent for a product for killing subsurface and

surface soil pathogens including nematodes, wire worms, cut worms, worms, insects, fungi and

plant and soil surface pests comprising an extract derived from the plant Tagetes minuta exists in

USA since 1997 (patent no. US5662915 A, 1997). According to the patent the extract is a natural

product, i.e. derived from the plant Tagetes minuta. It does not pose a threat to the environment

and is no danger to man. The insecticidal and fungicidal activity of floral, foliar and root extracts

and Tagetes minuta essential oil have also been extensively studied. The studies have highlighted

the effectiveness of the plant as a pesticide (Weaver, et al., 1994; Sadia, et al., 2013; Koul, et al;

2008; Padin, et al. 2013).

Fig.2.8. Tagetes minuta


25

2.7 Gynandropsis gynandra -Cleomes gynandra (L.) Brig. (Cruciferaceae, Brassicaceae)

Gynandropsis gynandra (syn. Cleome gynandra L.) is a herb used as a local bitter vegetable

(Chisaga, Spider flower, Cat’s whiskers). It is a glandular or almost hairless annual with 3-7

obovate to elliptic leaflets ; petal white, pale pink or lilac measuring 10-20 mm long. In some

areas it was considered as a weed distributed along roadsides and on dry bush land that grow in

soils with high organic matter (Agnew and Agnew, 1994). In Kenya it has become a common

leafy vegetable utilized mainly in Western Kenya, Rift Valley, Nyanza and main towns where

metropolitan populations exist. The leaves are bitter and are said to be high in calcium and has

medicinal value (Plate 2.9).

It has been used as an intercrop to control pests in vegetables (Gachu, et al., 2012). Intercropping

French bean with spider plant, for example, significantly reduces the population of spider mites

on the beans. Besides the direct effect on thrips population associated with spider plant, it was

also recorded to be a host for Orius spp. a natural enemy of thrips (Waiganjo et al., 2007).

Gynadropsis gynandra has also been recorded to have insecticidal, anti-feedant and repellent

characteristics. The ethanol extract is insecticidal to painted bug (Bagrada cruciferatum Kirk.)

and diamond back moth (Plutella xylostella L.). It also has antifeedant activity against tobacco

caterpillar (Spodoptera litura F.) while the seed extract has insecticidal effects against brinjal

aphids (Aphis gossypii Glov.) (Cheya and Mnzawa, 1997).

Companion planting of Cleome gynandra of Kenyan origin, in beds of cut-flower roses reduced

significantly red spider mite (Tetranychus urticae Koch) infestation without any detrimental

effect on productivity or flower quality. The potential benefits of such companion planting for

26

growers of field roses and those involved in some domestic markets have been enumerated

(Nyalala and Grout, 2007).

Fig. 2.9. Spider plant, Gynandropsis gynandra


27

CHAPTER THREE

EFFECT OF BOTANICAL PESTICIDES ON FRENCH BEAN INSECT PESTS

(APHIDS, THRIPS AND WHITEFLIES)

3.1 Abstract

French bean Phaseolus vulgaris L. is an important crop in Kenya mainly grown by small holder

farmers in various parts of the country. Approximately 50,000 small holder families are directly

or indirectly involved in its cultivation, producing about 80% of the crop in the country.

However, its production is faced by many challenges which include pest and diseases, high cost

irrigation systems, seeds and chemicals.The objective of the study was to evaluate the

effectiveness of the botanical pesticides Tithonia (Tithonia diversifolia), Tephrosia (Tephrosia

vogelii), Tagetes (Tagetes minuta) and spider plant (Gynandropsis gynandra) in the controlling

insect pests (thrips, aphids and whiteflies) in French bean field.

The botanical pesticides were extracted using water to give 10% w/v based on powder and were

sprayed on the French beans on a weekly basis. Data collected from plant extracts were

compared with a synthetic pyrethroid (Decis) and a commercial pesticide derived from neem

product (Nimbecidine). The experimental design was a Randomized Complete Block Design”

(RCBD) with seven treatments assigned randomly per block and replicated three times.

Data was collected on a weekly basis where and the population was assessed from 5 flowers per

plant on 5 plants randomly selected in the middle of each plot while aphids and white flies were

assessed in the same manner but from 3 leaves and 3 plants.

The botanical extracts had a significant reduction of pests compared to the control

Tephrosia botanical extract was the most effective followed by Tithonia. The two, Tephrosia and

Tithonia, were not different in their effect compared to commercial pesticides (Decis and

28

Nimbecidine) in reducing insect (aphids, thrips and whiteflies) population densities. The

botanical extracts can be used as an alternative to chemical control to reduce pest population

sustainable production of French beans.

3.2 INTRODUCTION

3.2.1 Pest management in French beans

Arthropod pests are the major constraints contributing to high yield loss, while high cost of

inputs (certified seeds, labour and fertilizers) make farmers produce French beans in small areas

ranging from 0.25 – 2 acres (Nderitu et al., 2008; Makokha et al., 2001). Continuous production

of the crop throughout the year coupled by poor pests control strategies encourages pests and

diseases to build up (Makokha et al., 2001). The French bean is attacked by several pests and

diseases which include bean fly (Ophiomya spp), flower thrips (Megalurothrips sjostedti

Trybom), (Frankliniella occidentalis Pergade), (Frankliniella schultzei Trybom), bean aphid

(Aphis fabae Scopoli), red spider mites (Tetranychus spp), African boll worm (Helicoverpa

armigera Hurbner), legume borer (Maruca testularis Geyer) and white flies (Bemisia tabaci). It

is estimated that damage due to thrips could be as high as 70% in French beans in Kenya and

Uganda (Lohr and Machalik, 1995, ICIPE, 2011).

The pests are mainly controlled by use of chemicals. Some farmers control the pests by

drenching twice within the two weeks after emergence while other farmers spray up to four times

during the first four weeks and many insecticides are also used to control thrips in order to

maintain the high quality demanded by the export market (Misheck, 2011; PCPB, 2014). Routine

spraying every one or two weeks ending up in spraying 8 to 15 times per French bean season is

common (Nderitu,et al., 2001). High use of pesticides has also been found to intestify spider

mites infestation (Seif et al., 2001). However, conventional pesticides are expensive, result in

29

ecological pollution, health hazard, cause insect pest populations to increase and lead to the

development of resistance to the pesticides and destruction of natural antagonist (Isman, 2008).

Botanical insecticides could lead to reduction of the undesirable effects of chemical insecticides

in pest management in French beans.

Although botanical extracts have insecticidal properties, their efficacy in controlling of pests in

various crops remains largely unknown (Adebayo and Gbolade, 1994). Sustainable pest

management is a prerequisite to farming in developing countries of Africa with economic risks

and uncertainties and harsh climatic conditions (Schwarb et al., 1995). There is renewed interest

in application of botanical pesticides for crop protection. Scientists are working to protect insect

infestation by indigenous plant materials (Roy et al.,2005). Botanical pesticides are

biodegradable (Devlin and Zeltel, 1999) and their use in crop protection is a practical sustainable

alternative. They maintain biological diversity of predators and reduce environmental

contamination and human health hazards (Grange and Ahmed, 1988). Research on active

ingredients, pesticide preparations, application rates and environmental impact of botanical

pesticides are a prerequisite for sustainable agriculture (Buss and Park-Brown, 2002). This will

provide standards for botanical pesticides use.

The objective of the present study was to determine the effect of botanicals, namely Tagetes

(Tagetes minuta), Spider plant (C.gynandra), Tithonia (Tithonia diversifolia) and Tephrosia

(Tephrosia vogelii) water extracts, on flower thrips, whiteflies and aphids affecting French

beans.

30

3.3 Materials and methods

3.3.1. Experimental site

The study was carried out at the College of Agriculture and Veterinary Science (CAVS) Kabete,

Field Station Farm, University of Nairobi between November 2012 and July 2013. The site is

about 1800 m above sea level. The soils are well drained, deep, reddish brown to dark red

(nitosols) developed from Limuru trachite, (Michieka, 1977). The area receives an annual

rainfall of about 1000 mm and experiences average temperatures of 230C (Wambua, 2004).

3.3.2 Crop establishment

The experiment was laid out in a randomized complete block design (RCBD) in plots of 3 m by

2.7 m replicated three times (Fig. 3.1). The plots were separated by 0.5 m and blocks separated

by 1 m. The variety of French bean planted was the Slender Green chosen because of its

availability in the market at the time when the experiment was done. The spacing of the crop was

50 cm, between rows and 10 cm between plants. The treatment application was done once in a

week to control thrips, whiteflies and aphids. The experiments were carried out in relay for three

crop cycles from November 2012 to July 2013.

T2 T4 T7 T1 T5 T6 T3

T4 T1 T5 T3 T2 T7 T6

T6 T2 T3 T7 T4 T1 T5

Fig. 3.1 Layout of the treatments in the field

T= Treatment, T1-tithonia, T2-tagetes, T3-tephrosia, T4-spider plant, T5-nimbecidine, T6-decis

and T7-control.

Di-ammonium phosphate (DAP) fertilizer was applied during planting at the rate of 133kg per

hectare. A similar amount of calcium ammonium nitrate (CAN) was used for top dressing at 35

31

days after crop emergence. Weeding was done twice during the growing period, first two weeks

after emergency and three weeks after the first weeding Fig. 3.1 shows a plot of French beans

after the 2nd weeding while Fig. 3.2 shows the French beans with pods.

3.3.3 Preparation of extracts, decis and nimbecidine

Plant materials (leaves) of the selected botanical pesticides were collected from various regions

in Kenya where they were found abundantly. These included Tephrosia (Tephrosia vogelii) from

Nakuru, Tithonia (Tithonia diversifolia) from Kirinyaga, Spider plant (Cleome gynandra) from

Kisii and Tagetes (Tagetes minuta) from Nairobi. The materials were dried under the shade for

two weeks and then ground and packaged in polythene bags. The botanical pesticides were made

from dried leaves ground into powder. Briefly, about one l litre of water was heated to boiling,

removed from heat and 100 g of accurately weighed material put into the hot water for each

plant. The powder was infused (left in boiled water) in water for twelve hours and then filtered

with muslin cloth. The extracts were then made to volume (1 litre) using cold water to give 10%

w/v based on the powder and sprayed on the French beans on weekly basis. Previous work had

shown that 10% and 20% w/v of Tephrosia vogelii water extract was highly effective to certain

insects (McDavid and Lesseps, 1994; Adebayo et al., 2007). Decis 2.5 EC (25 g/L deltamethrin

emulsifiable concentrate) diluted at 20 ml/15L and Nimbecidine(0.03% azadirachtin emulsifiable

concentrate) at 0.5 ml/L were also sprayed. Water spray was used as the control.

3.3.4 Data collection and analysis

Before application, pre-treatment assessment of thrips, white flies and aphids were carried out.

The aphids and white flies were recorded from three leaves per plant randomly selected in the

middle of each plot and from three plants. Thrips population was assessed from 5 flowers per

plant on 5 plants and preserved in 50% alcohol in separate bottles for flower maceration,

32

identification and counting of thrips. The flower thrips (Megalurothrips sjostedti), (Frankliniella

occidentalis), (Frankliniella schultzei Trybom), were all recorded as thrips. The bean aphid

(Aphis fabae), and whiteflies (Bemisia tabaci) were also recorded. Treatment and assessment of

pest population was done weekly for a period of four weeks. The yield of French beans was

recorded for each treatment in each plot for every planting. Data analysis was carried out by

using GenStat Release 14.2 software.

Plate 3.1 Plot of French beans after the second weeding.


33

Plate 3.2 Plot of French beans with pods.


34

3.4 RESULTS

3.4.1. Effect of botanicals on aphids population in planting one ( Nov 2012 –Feb 2013)

In planting one, the effect of Decis on aphids was significantly different from all other treatments

and the control (p<0.05). The control plots had the highest mean of aphids (11) while Decis had

the least (2) aphid (Table 3.1). The mean number of aphids for tephrosia (3) was comparable to

that of Nimbecidine. The effect of spider plant and tagetes on aphids was not different from each

other.

Table 3.1 Mean number of aphids recorded on French bean in planting one

Sampling 1 2 3 4 Overall mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

1.7 3.0 3.7 7.1

1.1 2.1 3.0 5.2

4.3 7.4 9.9 12.9

5.0 8.2 11.7 15.3

1.2 2.0 3.8 4.3

1.1 1.7 2.3 3.3

6.8 8.4 12.2 16.8

3.9bc

2.9bc

8.6ab

10.1ab

2.8bc

2.1c

11.1a

P value

Lsd

Cv

<0.001

1.5

5.7%

Means with the same letters are not significantly different at p<0.05

3.4.2 Effect of botanicals on thrips population in planting one (Nov 2012-Feb 2013)

Tithonia and tephrosia extracts were able to reduce thrips populations significantly compared to

the control. In planting one, thrips were least recorded in the plots treated with Decis (6.7).

(Table 3.2). Tithonia, tephrosia extracts produced the same effects on thrips.

35

Table 3.2 Mean number of thrips recorded on French bean in planting one

Sampling 1 2 3 4 Overall

mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

3.7 5.3 11.8 12.3

1.7 4.3 13.3 13.2

5.1 9.4 17.1 19.1

6.6 8.4 17.3 22.6

3.9 4.2 12.4 12.4

3.0 4.1 9.2 10.6

8.8 10.3 18 22.9

8.3b

8.2ab

12.7ab

13.7ab

8.3ab

6.7b

15.0a

P value

Lsd

Cv

<0.001

1.4

4.5%


3.4.3 Effect of botanicals on whiteflies population in planting one (Nov 2012-Feb 2013)

There was no significant difference of the mean number of whiteflies found in plots treated with

spider plant, tagetes and the control (Table 3.3). Decis plots had the least mean number of

whiteflies (6) followed by nimbecidine (7), tephrosia (8) and tithonia (9). The mean number of

whiteflies for tephrosia and nimbecidine were not significantly different.

36

Table 3.3 Mean number of whiteflies recorded on French bean in planting one


mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

6.9 8. 3 8.7 11.4

6.9 6.6 7.4 9.2

13.8 15 17.2 20.2

13.3 15 22.2 24.8

5.6 6.3 7.3 8.0

5.0 5.0 5.7 7.0

14.4 18.3 21.6 24.9

8.6b

7.5bc

16.6a

18.8a

6.9bc

5.6c

19.8a

P value

Lsd

Cv

<0.001

5.4

6.2 %


3.4.4. Effect of botanicals on aphids population in planting two (March-June 2013)

In planting two, the most effective treatments were Decis, nimbecidine, tephrosia and tithonia

respectively. These were not significantly different from each other but they were significantly

different form those treated with tagetes, spider plant and the control (p<0.05) (Table 3.4).

Table 3.4 Mean number of aphids recorded on French bean in planting two


mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

3.0 5.7 4.3 8.3

2.3 5.0 5.7 6.3

6.0 10 13.3 13.3

6.7 9.0 15.5 15.7

2.7 4.0 5.7 6.3

1.7 3.7 4.7 6.7

8.0 9.7 17.3 17.3

5.3b

4.8b

10.7a

11.7a

4.7b

4.1b

13.1a

P value

Lsd

Cv

<0.001

1.2

2.3%


37

3.4.5 Effect of botanicals on thrips population in planting two ( March –June 2013)

Decis reduction on thrips populations was significantly different from that of other treatments

used. Decis had the least number of thrips while the control had the highest. The effect of

tithonia and tephrosia on thrips was comparable (Table 3.5).

Table 3.5 Mean number of thrips recorded on French bean in planting two


mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

3.0 5.7 14.3 16.7

2.3 5.0 14.0 16.3

6.0 10.0 17.3 20.3

6.0 8.0 19.3 22.7

2.7 4.0 11.0 16.3

1.7 3.0 7.3 14

8 9.7 18 22.2

9.2abc

9.4abc

13.0ab

14.0ab

8.5bc

6.5c

14.5a

P value

Lsd

Cv

<0.001

1.2

4.2%


3.4.6 Effect of botanicals on whiteflies population in planting two ( March –June 2013)

The plant extracts (tithonia and tephrosia) significantly p< 0.05 reduced whitefly populations

compared to the control in season 2. Decis had the least mean of whitefly populations compared

to the control which had the highest. Again tithonia, tephrosia and nimbecidine effect on

whiteflies was not significantly different from that of Decis.There was no significant difference

between the mean populations of control, tagetes and spider plant (Table 3.6). Tithonia,

tephrosia, nimbecidine and decis mean populations significantly differed with those of spider

plant, tagetes and the control. Decis and tephrosia were the most effective.

38

Table 3.6 Mean number of whiteflies recorded on French bean in planting two


mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

0 1.3 2 4.7

0 0 2 3

1.3 2.3 5.7 8

2.0 2.3 6.7 9

0 0.3 2.3 1.7

0 0 1 1

2.3 4.7 6 10

2.0b

1.2b

4.2a

5.0a

1.1b

0.5b

5.8a

P value

Lsd

Cv %

<0.001

0.72

1.9


3.4.7 Effect of botanicals on aphids population in planting three ( April - July 2013)

The number of aphids recorded in planting 3 is shown (Table 3.7). Tagetes and spider plant

extracts were the least active treatments showing high mean numbers of aphids. Tephrosia (1)

and tithonia (2) extracts were very active as compared to tagetes and the spider plant.

Table 3.7 Mean number of aphids recorded on French bean in planting three


mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

0.7 1.0 2.0 6.0

0.3 0.3 0.3 3.7

5.7 8.3 11.3 17.3

7.0 11.7 14.3 22.7

0 0.3 2.3 2.3

1.3 0.3 1.7 1.7

9.3 11.0 14.0 24.3

2.4c

1.2c

10.7b

13.9ab

1.2c

1.0c

14.7a

P value

Lsd

Cv

<0.001

1.0

4.5%


39

3.4.8 Effect of botanicals on thrips population in planting three ( April - July 2013)

Plots treated with tephrosia extract had the least number of thrips (8) compared to the other

extracts. Its effect was comparable to Decis and nimbecidine (Table 3.8). Spider plant (15) and

Tagetes (14) had low insecticidal activity and were comparable to control (15).

Table 3.8 Mean number of thrips recorded on French bean in planting three


mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

3.0 5.0 13.3 16.3

1.0 3.0 12.0 15.3

5.7 8.3 17.7 22.7

7.7 10.0 17.3 25.0

3.0 4.0 11.3 16.7

3.0 4.0 10.3 15.3

9.3 11.0 18.3 22.0

9.4bc

7.8c

13.6ab

14.8ab

8.6c

8.2c

15.2a

P value

Lsd

Cv

<0.001

1.2

3.1%


3.4.9 Effect of botanicals on whiteflies population in planting three ( April - July 2012)

Table 3.9 shows that tithonia, tephrosia, nimbecidine effects on pests were significantly different

from tagetes and spider plant (p<0.05). While the control and tagetes had a mean of 15 and 10

whiteflies respectively. Plots treated with Decis had a mean of only one insect. The effect of

Decis, nimbecidine, tephrosia and tithonia were not significantly different from each other

(p<0.05).

40

Table 3.9 Mean number of whiteflies recorded on French bean in planting three


mean

Treatment

Tithonia

Tephrosia

Tagetes

Spider plant

Nimbecidine

Decis

Control

1.0 2.3 4.7 7.0

0.3 1.0 2.3 5.0

5.7 9.3 12.3 13.7

7.0 11.0 17.0 25

0 0.7 3.7 3.3

0 0.3 1.3 3.0

9.3 11.0 19.7 21.7

3.8c

2.2c

10.2b

15.0a

1.9c

1.2c

14.9a

P value

Lsd

Cv

<0.001

1.4

6.2%


3.4.10 Yield of French beans in planting one

There was a general increase of yields of French beans among the plant extract treatments.

Nimbecidine had the highest yield compared to the rest of the treatments (Fig. 3.2).


Fig 3.2 Yield of French beans in planting one

0

100

200

300

400

500

600

700

800

900

1000

yie

ld o

f Fr

en

ch b

ean

s (

g)

Treatment

a

ba ba ba ba

c

a

41

3.4. 11 Yield of French beans in planting two

Decis treated French beans had a significant higher yield in planting two compared to other

treatments and the control (p<0.05 ). Nimebicidine did not show any significant difference in

yield compared to tephrosia (Fig. 3.3). Nimbecidine and tephrosia French bean yields did not

significantly differ from each.


Fig 3.3 Yield of French beans in planting two

3.4.12 Yield of French beans in planting three

In planting three, Decis had significantly higher French bean yield compared to other treatments

and the control (p<0.05). Nimbecidine, Tithonia and Tephrosia did not show any significant

differences in French bean yield (Fig. 3.4). Spider plant, tagetes and the control were comparable

in the yield of French beans and were significantly different from that of Decis and the rest of the

treatments.

0

200

400

600

800

1000

1200

1400

yie

ld o

f Fr

en

ch b

ean

s (g

)

Treatment

a

b b bc

cd cd d

42


Fig 3.4 Yield of French beans in planting three

3.5 Discussion

Pesticide application (both synthetic and botanical) has been shown to control insect

infestations and increase yield of French bean in the present work. The results show that use of

botanical pesticides could effectively manage thrips, whiteflies and aphids. Spraying Tephrosia

vogelli and Tithonia diversifolia water extracts controlled the pest populations in French beans

compared with the synthetic pesticide Decis and Neem derived product (Nimbecidine).

Application of botanical pesticides, Tephrosia vogelii and Tithonia diversifolia proved to be

more effective against the investigated insect pests (aphids, thrips and whitefies). The major

ingredients in T. vogelii are rotenone, dequelin, alpha-toxicarol, tephrosin, sarcolobin and 5-

methoxyisolonchocarpin which may have been responsible for the insecticidal and antifeedant

activity (Carlson and Tallent, 1970; Belmain, et al., 2012). These are the compounds responsible

for the activity of tephrosia extract.. A number of compounds including sesquiterpenoids and

sesquiterpene lactones such as tagitinin, tirotundin, tithofolinolide, 3α-acetoxydiversifolol, 3β-

0

200

400

600

800

1000

1200

1400

1600

1800w

eig

ht

of

Fre

nch

be

ans

(g)

Treatment

a

b b b

c c c

43

acetoxy-8β-isobutyryloxyreynosin and their derivatives have been isolated from Tithonia

diversifolia (Lee, et al., 2011; Gu, et al., 2002; Garcia and Guillermo, 2006; Zhou, et al., 2000;

Baruah, et al., 1979). Some of these compounds could be responsible for the insecticidal activity

of tithonia extract. Commercial pesticide (Decis, as synthetic pyrethroid, deltamethrin) and

nimbecidine (derived from neem oil) performed best as expected. Tephrosia and tithonia extracts

were as effective as Decis and nimbecidine, while Tagetes minuta and Gynadropsis gynadra

(Cleome gynadra) demonstrated very low insecticidal activity on the pests and were similar with

the control.

This study indicates that tithonia extract was very effective and in some instances was sometimes

as effective as Decis and nimbecidine insecticides. The effect of tithonia water extract on thrips

and whiteflies on French beans is reported here for the first time. The powder and ethanol

extracts of Tithonia diversifolia leaves have been shown to have anti-ovipositional, ovicidal and

knock down properties on cowpea seed bruchid (Adedire and Akinneye, 2004). Its extract is said

to be as effective as the nematicide carbofuran in the management of root-knot nematode

(Akpheokhai, et al., 2012). Moreno (1991), considered high concentation of tithonia water

extract to be potentially useful in blocking rapid reproduction of aphids at 59,38 and 19.5% kill

when sprayed with 100,75 and 50% water extract, respectively). Water extract of Tithonia

diversifolia has been shown to be the best for the control of Periplanata americana over organic

extracts (Ambama, 2013). The present study showed that 10% w/v of tithonia and tephrosia

extracts had a significant effect on French beans in yields and thrips number on the flowers

compared with the other plants extracts and the control. This study has given a comprehensive

report on pesticidal effect of water extract of Tephrosia on the three tested insects (Aphids,

Thrips and Whiteflies) in French beans. Work done by Alao, et al., (2011) reported that

http://pubs.acs.org/action/doSearch?ContribStored=Baruah%2C+Nabin+C.


44

application of Tephrosia vogelii and Petiveria alliacea was effective against Riptortus dentipes,

Megalurothrips sjostedti and Megalurothrips vitrata in cowpea. The study conducted by

(Adebayo, et al., 2007) at the research farm in Nigeria using T. vogelii and P. alliacea to control

insect pests (Maruca testularis) on cowpeas showed the potential of these plants in controlling

pests. Another study by (Lao, et al., 2011) evaluating the natural toxicants from Tephrosia

vogelii and Petiveria alliacea on Megalurothrips sjostedti and Apion varium of cowpea (Vigna

unguiculata (L) Walp) showed that the two insect pests were effectively controlled by the

botanical insecticides compared with untreated plants. Also, the plant extracts at 20% and 10%

v/v significantly protected cowpea pods and grains from the insect damage. However, higher

grain yield was obtained from the plant treated with 20% v/v compared to those treated with

10%, 5% v/v and untreated plants. combination of the two plant extracts at 20% v/v had the same

efficacy with synthetic insecticide (Decis) (Lao, et al., 2011). Results obtained from the present

study confirm that tephrosia water extract can be used in the control of insects in French beans.

The low insecticidal activity of tagetes may be attributed to the fact that the pesticidal activity of

the plant resides in its essential oil which could have evaporated during the hot water extraction

or due to the fact that the activity may be due to non-polar compounds which cannot be extracted

with water (Dinesh, et al., 2014, Perich, et al., 1995; Phoofolo, et al., 2013; López, et al., 2011;

Singh et al., 2003; Weaver, et al., 1994; Maradufu, et al., 1978). It was not clear why the spider

plant did not have any effect on insects. There is a possibility that it could be due to the

extraction method used (Cheya and Mnzawa, 1997). This is because it has been used as an

intercrop to repel insects such as aphids on cabbages, Kales and roses (Waiganjo, et al., 2007).

45

Tephrosia vogelii is widely spread in Kenya and grows well in areas where French beans are

cultivated so this plant can readily be grown by farmers for use as a pesticide. However, the plant

is quickly being uprooted in the new fishing area as the leaves paralyse the fish if sprinkled into

the fish ponds (Neil, 2013; Akpa, 2010). Tithonia diversifolia is planted as hedges in many

homes and therefore does not present the same challenge as Tephrosia.

This is the first comprehensive report on the effect of water extract of tephrosia on the three

tested insects (Aphids, Thrips and Whiteflies) in French beans. However, work done earlier on

French beans (string bean) had shown that high concentrations of Tithonia diversifolia leaf water

extract solution resulted in high mortality on aphids and reduced root damage caused by Aphis

sp.,Crocidomia binotalis, Ophiomyia (Melanogramxya) phaseoli and a borer species (Moreno

1991). While the Aphids species was not specified, there is no report on pesticidal activity of

Tithonia diversifolia on Megalurothrips sjostedti, Frankliniella occidentalis and Bemisia tabaci

on French beans.

46

CHAPTER FOUR

EFFECT OF COLOURED STICKY TRAPS IN MANAGEMENT OF FLOWER THRIPS,

WHITEFLIES AND APHIDS AFFECTING FRENCH BEANS

4.1 Abstract

A field experiment was conducted to evaluate the effect of different coloured sticky traps on the

monitoring and management of selected insect pests of French beans. The experiment was laid

out in a Randomized Control Block Design and was set up at Kabete Campus, University of

Nairobi experimental farm. Different colour sticky traps (Blue, Yellow and clear) were used as

treatments, decis and water were used as control. Thrips population was assessed from 5 flowers

per plant on 5 plants randomly selected in the middle of each plot. The aphids and white flies

were assessed in the same manner but from 3 leaves and 3 plants. Data was analysed. The target

insect species were Western flower thrips (Frankliniella occidentalis), commom blossom thrip

(Frankliniella schultzei), African bean flower thrips (Megalurothrips sjostedti) and whiteflies

(Bemisia tabaci), Black bean aphid (Aphis fabae); the most common pests on French beans. Data

was analysed to assess the effect of colour on the target pests

The plots where the blue sticky color traps had been mounted had less of thrips than the plots

with yellow traps. Plots treated with Decis had almostvery few thrips in the flowers. Although

the total number of aphids recorded did not have any significant difference over the three

plantings for yellow and blue traps, there was a signicant difference for thrips and whiteflies at p

<0.05.

Plots with yellow and blue sticky traps did not show any significant difference in yield of French

beans. The plots treated with Decis had the highest yields of at least about 1.4 higher than yellow

47

or blue traps mounted plots. These results imply that the farmer may apply reduced rates of

Decis thereby resulting in fewer negative effects on human health and reduced cost of

production.

4.2 INTRODUCTION

It is estimated that over 50,000 small holder families are directly or indirectly involved in French

bean cultivation in Kenya. About 80% of French beans in Kenya are produced by small scale

farmers (Nderitu et al., 2008). They are mainly grown for the export market as a source of

income for the family. According to SNV Netherlands Development Organization study, French

bean production employs 45,000 to 60,000 people (2012). Sixty percent of the workers are

women engaged in commercial farms and they dominate post harvest handling of French beans;

sorting, grading and in quality control. Farmers are always under pressure to meet standards on

environment, food safety, quality and traceability, occupation health and safety of workers

especially those set by the European Union which is the main market for French beans from

Kenya (Ogola, 2013; Goro, 2013).

Use of coloured sticky insect traps is another way of contributing to increased production of

French beans free of chemical residues. The information will encourage the farmers to use

readily available plant materials in the control of pests to improve productivity of French beans

in Kenya. In general yellow sticky traps are recommended for monitoring and reducing adult

leaf miners, moths, leafhoppers, whiteflies, aphids (winged forms) thrips and fungus gnats,

among other insect pests (Hoddle, et al., 2002). Thrips are also attracted to white and blue

colour. As the yellow colour attracts many insect species, including beneficial insects, yellow

sticky traps should be used only where necessary. Adult thrips can be monitored and in some

cases be reduced by mass trapping with coloured (blue, yellow or white) sticky traps in

48

greenhouses. Red sticky traps have been found to to be more effective on Tuta absoluta moths

(47%) compared with other trap colours (Taha, et al., 2012). Rodriguez-Saona, et al., (2012)

found that green coloured traps had the most attractive activity to blunt-nosed leafhoppers while

yellow traps were most attractive to sharp-nosed leafhoppers. Pasian and Lindquist (2009)

recommended yellow coloured traps for monitoring western flower thrips, whiteflies and fungus

gnats.

Western flower thrips (WFT), Franklinella occidentalis (Pergande) is considered the most

destructive insect pest of greenhouse-grown crops due to direct feeding damage to plant parts

such as foliage and flowers, and indirect damage by vectoring the tospoviruses; impatiens

necrotic spot and tomato spotted wilt virus (Cloyd, 2009). Furthermore, western flower thrips is

difficult to manage in greenhouse production systems due to a number of factors including broad

range of ornamental plants fed upon, high female reproductive capacity, rapid life cycle (egg to

adult), residence in cryptic habitats such as unopened terminal buds that protect them from

exposure to contact insecticides, and resistance to various insecticide chemical classes (Cloyd,

2009). As such, the management of WFT requires a holistic or complex approach, including the

concurrent implementation of scouting, cultural, physical, insecticidal, and biological strategies.

Greenhouse producers utilize sanitation and biological control practices to avoid solely relying

on insecticides. The advent of resistance among WFT populations worldwide has led to a general

interest among greenhouse producers in adopting the use of biological control as a long-term

strategy to deal with WFT, and still produce and sell quality produce (Bielza, et al., 2007). The

main technique used to scout for WFT adults is to place either blue or yellow sticky cards above

the crop canopy, although there is still disagreement on which color is the most attractive to

WFT (Cloyd, 2009).

49

Tests on sticky traps on thrips populations have revealed differential attraction, and published

results are not consistent. In some tests where sticky yellow and white traps were used, it was

reported that there were more Frankliniella occidentalis on white than on yellow traps (Kaas,

2005). Other reports comparing blue, white and yellow traps indicated higher catches for yellow

than for other colors (Kaas, 2005). In general blue sticky traps have been used for thrips

monitoring and yellow for whitefly, aphid and other insects. According to Kaas (2005) blue

sticky traps are significantly more attractive to thrips than yellow.

In Kenya some studies on sticky colored traps has been reported. A study by Muvea, (2011)

with French beans, blue sticky traps caught 2– 3.5 times as many thrips as yellow traps, and 22 –

29 times more than white traps. Furthermore, blue traps were most attractive to Megalurothrips

sjostedti (Trybom), Ceratothripoides brunneus (Bagnall) and Frankliniella schultzei (Trybom).

Hydatothrips adolfifriderici (Karny) were only attracted to yellow traps. Muvea (2011) also

indicated that blue and yellow traps were equally attractive to Frankliniella occidentalis

(Pergande) in tomato (Muvea, 2011). In another report based on the survey of Frankliniella

schultzei, F. occidentalis (French bean, capsicum and cucurbits), Thrips tabaci (onions and

crucifers), Ceratothripoides brunneus (tomato) and Megalurothrips sjostedti (French bean,

cowpea, common bean), it was recorded that most of the thrip species were attracted to blue-

coloured sticky traps than the yellow sticky traps (ICIPE, 2011). Kasina, et al., (2009), studied

the spatial distribution of flower thrips, Frankliniella occidentalis (Pergande) and

Megalurothrips sjostedti Trybom, on French beans (Phaseolus vulgaris L.) in Kenya. The build

up and population dynamics were monitored using sticky blue colour traps and sampling of

50

leaves and flowers in two plantings. The study showed that a combination of monitoring with

sticky traps and proper sampling would contribute to sustainable thrips management.

Blue sticky traps with and without pheromone capsules have also been used to monitor and

control Frankliniella occidentalis (Elimem et al., 2014). However, the pheromone enhances the

effect of blue sticky traps in catching thrips species such as F. occidentalis and Thrips tabaci

(Mateus, et al., 2012). According to Zepa-coradini, et al., (2010) yellow sticky traps attract a

large number of Frankliniella occidentalis adults and can be used directly in controlling or

monitoring this pest population. In an experiment to monitor western flower thrips

(Frankliniella occidentalis), population in a greenhouse with tomato crop, blue and yellow traps

had the highest attractiveness compared to other colors (white, red and clear). Among the colors

used in this study, blue proved to be the most effective (Covac, et al., 2012). Yellow, white, and

blue sticky cards when tested in an avocado orchard for their attractiveness to Scirtothrips

perseae, Frankliniella occidentalis and Franklinothrips orizabensis, yellow cards were most

attractive to Scirtothrips perseae and white cards captured mostly Franklinothrips orizabensis

and Frankliniella occidentalis (Hoddle, et al., 2002). Experiments conducted by Yudin, (1987)

to determine color preference of thrips, aphids and leafminers in lettuce farms in Hawaii

indicated that white traps significantly caught more thrips than 14 other colors tested.

Frankliniella occidentalis (Pergande) was the predominant thrips species trapped. More adult

and larval thrips were associated with plants with tomato spotted wilt disease than with healthy

plants during later weeks of lettuce growth. The mean number of aphids and leafminers trapped

did not indicate any conclusive preference of these insects for a particular color.

51

In a study mounted by Oseto (1999) flower thrips, Frankliniella tritici, were attracted to white

sticky traps while aphids, Aphis spiraecola, were attracted to yellow traps.

A study to determine the effectiveness of sticky trap designs with different colours for trapping

alate whitefly, Bemisia tabaci using yellow, blue, green, red, white and black, yellow was the

most attractive colour to these whiteflies and therefore had the highest number of whiteflies

caught compared to the other colours (Idris, et al., 2012). The sweet potato whitefly, Bemisia

tabaci densities in the greenhouse with yellow sticky traps were significantly lower than the

greenhouse without traps. In the field, the yellow traps did not have a significant impact on the

population dynamics of adult and immature potato whiteflies (Yaobin, et al. 2012). The

objective of the present study was to assess the effect of different colored sticky traps to

management of thrips, whiteflies and aphids on French bean.

52

4.3 MATERIALS AND METHODS

4.3.1 The Experimental site

The study was carried out at the College of Agriculture and Veterinary Science Kabete, Field

Station Farm, University of Nairobi between November 2012 and July 2013 (First planting:

November 2012- February 2013, second planting: March –June 2013 and third planting: April –

July 2013). The site is about 1800 m above sea level. The soils are well drained, deep, reddish

brown to dark red (Nitosols) developed from Limuru Trachite (Michieka, (1977). Kabete area

receives an annual rainfall of about 1000 mm and experiences average temperatures of 230C

(Wambua, 2004).

4.3.2 Experimental layout

Commercial certified seed of French beans (Slender Green variety) was planted between

November 2012 and July 2013. Demarcation into blocks and making of trenches were done

manually (Fig 4.1). The crop was rain-fed and irrigation was done to supplement when

necessary. The experimental layout was RCBD with four replicates. Different coloured traps

were used as treatments. These were blue, yellow and clear. The traps were placed in the middle

of the plots 60 cm above the ground arranged in a triangular design at 0.5 m apart four weeks

after planting.

T4 T2 T1 T5 T3

T2 T3 T4 T1 T5

T5 T1 T3 T2 T4

Fig. 4.1 Layout of the trap treatments in the field

T= Treatment, T1-Decis, T2-Clear, T3-Control, T4-Yellow and T5-Blue.

Di-ammonium phosphate (DAP) fertilizer was applied during planting at the rate of 133 kg per

hectare. Weeding was done twice during the growing period, first two weeks after emergence.

53

Plate. 4.1. Plot of French beans with Colored Traps

Source :FN Mwangi 2013

Plate 4.2 Mounted colored yellow trap


54

Plate 4.3. Blue colored trap with pests stuck on it.


Randomized Complete Block Design (RCBD) was used with four replicates. The traps were

mouted 0.5 m from each other and 60 cm from the ground.

Assessment of the colored traps was undertaken during the period of November 2012 to July

2013.

4.3.3 Data collection and analysis

Before mounting the coloured traps, assessments of thrips, whiteflies and aphids were carried

out. The aphids and whiteflies were recorded on three leaves per plant randomly selected in the

middle of each plot from three plants. Thrips population was assessed in the same manner from

5 flowers per plant on 5 plants randomly selected in a plot; the flowers were preserved in 50%

alcohol in separate bottles for flower maceration, identification and counting of thrips. The

flower thrips (Megalurothrips sjostedti), (Frankliniella occidentalis), (Frankliniella schultzei

Trybom), were all recorded as thrips. The bean aphid (Aphis fabae), and whiteflies (Bemisia

55

tabaci) were recorded separately. Pest population data was done weekly for a period of four

weeks and the traps were replaced weekly with new ones (Figs. 4.1 – 4.3). The yields of French

beans were recorded for each planting. Data analysis was carried out by using GenStat Release

14.2 software.

4.4 RESULTS

4.4.1 Effect of coloured traps on aphids in planting one (Nov. 2012- Feb 2013)

Decis treated plots had significantly lower aphid populations recorded compared to other

treatments and the control (p<0.05). Plots with mounted yellow and blue sticky colors did not

show a significant difference in mean number of aphids in the plots. The control plots had the

highest aphid infestation (13) while Decis plots had no aphids. In the plots where blue and

yellow traps were mounted 3 and 5 aphids were recorded, respectively (Table 4.1).

Table 4.1 Mean number of aphids recorded on French bean in planting one


mean

Treatment

Blue

Yellow

Clear

Control

Decis

2.8 2.3 3.8 4.7

7.1 2.1 4.3 5.7

11.8 6.4 7.3 7.8

10.4 11.7 14.8 15.8

0 0 0 0

3.4c

4.8c

8.3b

13.2a

0.0d

P value

Lsd

Cv

<0.001

2.5

10.1%


56

4.4.2 Effect of coloured traps on thrips on planting one (Nov. 2012- Feb 2013)

Decis treated plots had significantly lower number of thrips compared to the other treatments and

the control (p<0.05). Plots with yellow colored traps had lower number of thrips compared to

other coloured traps (Table 4.2).

Table 4.2 Mean number of thrips recorded on French bean in planting one


mean

Treatment

Blue

Yellow

Clear

Control

Decis

78 62.2 69.4 153.1

84.4 66.3 78.6 88.9

96.8 81.6 90.3 115.3

167.2 187.1 222.0 333.3

0.1 1.0 1.2 0.6

90.7d

79.6c

96.0b

227.2a

0.7e

P value

Lsd

Cv

<0.001

23.7

10.9%


4.4.3 Effect of coloured traps on whiteflies in planting one (Nov. 2012- Feb 2013)

In planting one there was only one whitefly recorded in the plots treated with Decis (Table 4.3).

Although 18 thrips were recorded in the plots having blue coloured traps, plots with yellow traps

had a mean of 50 whiteflies while Decis had a mean of 1 whitefly. The control had the highest

mean number of whiteflies (120) and was significantly p < 0.05 different from the coloured

traps. Clear traps had the 2nd highest mean of whiteflies (80) and was different from all other

traps including Decis and the control.

57

Table 4.3 Mean number of whiteflies recorded on French bean in planting one


mean

Treatment

Blue

Yellow

Clear

Control

Decis

18.7 14.4 14.0 24.0

40.2 53.4 40.8 68.0

53.8 43.7 54.3 94.1

109.3 88.7 90.7 192.2

0.4 0 3.4 0.4

17.9cd

50.6c

61.5b

120.2a

1.1d

P value

Lsd

Cv

<0.001

12.5

3%


4.4.4 Effect of coloured traps on aphids in planting two (March 2013- June 2013)

The Decis treated plots had significantly lower aphid population in planting two compared to the

coloured traps and the control(p<0.05) (Table 4.4). There was no significant difference between

blue and yellow traps regarding the aphids recorded.The control plots had the most mean number

of aphids (13). Plots treated with Decis had no aphids.

Table 4.4 Mean number of aphids recorded on French bean in planting two


mean

Treatment

Blue

Yellow

Clear

Control

Decis

2.7 2.3 4.0 4.7

4.3 1.7 4.7 5.7

7.3 8.7 10.3 10.3

10.0 11.7 15.3 16.3

0 0 0 0

3.4c

4.1c

9.2b

13.3a

0.0d

P value

Lsd

Cv

<0.001

0.962

3.6%


58

4.4.5 Effect of coloured traps on thrips in planting two (March 2013- June 2013)

The plots mounted with blue sticky traps had significantly lower mean number of thrips (58)

compared to the yellow traps (83) in planting two (p<0.05). The control had the most mean

number thrips (204) while the Decis plots had only one thrip.

Table 4.5 Mean number of thrips recorded on French bean in planting two


mean

Treatment

Blue

Yellow

Clear

Control

Decis

74.0 46.3 52.3 60.7

100.0 71.0 78.7 81.7

125.3 107.0 115.7 120.0

163.0 189.7 221.0 224.0

0 0.3 1.0 0.3

58.3d

82.8c

117.0b

204.4a

0.5e

P value

Lsd

Cv

<0.001

0.962

3.6%


4.4.6 Effect of colured traps on whiteflies in planting two (March 2013- June 2013)

The control plots had the most mean number of whiteflies (121) in planting two (Table 4.6). The

mean number of whiteflies in plots with blue colored traps (21) and yellow traps (39) were

significantly different close. Decis had the least mean number of whiteflies (1) in planting two.

59

Table 4.6 Mean number of whiteflies recorded on French bean in planting two


mean

Treatment

Blue

Yellow

Clear

Control

Decis

20.0 16.0 23.0 23.0

39.3 46.3 31.7 40.3

56.7 70.3 87.0 117.7

113.3 88.7 90.7 191.0

0.7 0 3.7 0

20.5cd

39.4c

82.9b

120.9a

1.1d

P value

Lsd

Cv

<0.001

19.58

7.0%


4.4.7 Effect of coloured traps on aphids in planting three (April 2013- July 2013)

In planting three, aphid populations in the control plots (13) were comparable with those in the

clear sticky traps plots (14 aphids). Although the plots treated with Decis had no thrips, there was

no significant difference between aphid population in Decis and those with blue colored sticky

traps. (Table 4.7).

Table 4.7 Mean number of aphids recorded on French bean in planting three


mean

Treatment

Blue

Yellow

Clear

Control

Decis

2.7 2.3 4.0 4.7

14.0 3.0 4.7 5.7

27.3 8.7 9.3 9.7

10.3 11.7 13.7 14.7

0 0 0 0

3.4b

6.8ab

13.8a

12.7a

0.0b

P value

Lsd

Cv

<0.001

6.92

26.2%


60

4.4.8 Effect of coloured traps on thrips in planting three (April 2013- July 2013)

In planting three, coloured and clear traps had a significant effect on thrip populations compared

to the control. The mean thrip population recorded in the decis plots was different compared to

the blue, yellow and clear traps (p<0.05). The coloured traps mean numbers were all different

from each other (Table 4.8).

Table 4.8 Mean number of thrips recorded on French bean in planting three


mean

Treatment

Blue

Yellow

Clear

Control

Decis

80.3 53.3 48.7 48.0

103.7 71.0 77.0 89.0

126.7 92.0 101.3 118.0

168.0 182.0 221.0 236.7

0.8 1.3 1.3 0.7

62.6d

85.2c

109.5b

201.9a

0.8e

P value

Lsd

Cv

<0.001

16.83

13.7%


4.4.9 Effects of coloured traps on whiteflies in planting three (April 2013- July 2013 )

In planting three, there were significant differences in the mean whiteflies populations recorded

in control the plots (120) compared to that in clear sticky traps (77) (p<0.05). Whitefly mean

numbers recorded in plots with blue coloured traps were higher than those recorded in yellow

traps (Table 4.9). Similarly, the mean whiteflies population in the blue coloured trap plots was

not different from the Decis plot. However, there was a difference between yellow trap on

whitefly mean population and Decis plots whitefly population.

61

Table 4.9 Mean number of whiteflies recorded on French bean in planting three


mean

Treatment

Blue

Yellow

Clear

Control

Decis

18.0 18.0 11.7 23.0

40.7 50.3 25.3 39.7

57.3 55.7 69.3 126.0

107.3 88.7 90.7 194.7

0.3 0 3.3 0.7

17.7cd

39.0c

77.1b

120.3a

1.1d

P value

Lsd

Cv

<0.001

19.7

0.4%


4.4.10 Yield of French beans in planting one

Fig. 4.2 shows that there was significant difference in yield for the plots treated with Decis

compared to coloured traps and the control in planting one (p<0.05) and there was no significant

difference between blue, yellow and clear traps in yield. In this planting the Decis treated plots

yielded an average of 1424 g (1,758 kg/ha) while blue and yellow yielded 958 g (1,183 kg/ha)

and 904 g (1,116 kg/ha), respectively. Control had the least mean yield of 559.1 g (690 kg/ha).

62


Fig. 4.2 Yield of French beans in planting one

4.4.11 Yield of French beans in planting two

In planting two Decis plots yielded an average of 1482 g (1,830 kg/ha) while blue and yellow

treatments produced 1030 g (1,272 kg/ha) and 988 g (1,220 kg/ha) respectively (Fg. 4.14). There

was no significant difference in the yields of French beans between the plots with blue and

yellow traps and there was no significant difference in yields between plots with clear traps and

the control. Control had the least yield of 600 g. (740 kg/ha).

0

200

400

600

800

1000

1200

1400

1600

Decis Blue Yellow Clear Control

Yie

ld o

f Fr

en

ch b

ean

s (g

)

Treatment

a

b b

bc

c

63


Fig. 4.3 Yield of French beans in planting two

4.4.12 Yield of French beans in planting three

A similar picture on yields which was recorded in planting two was also observed in planting

three (fig.4.4). In planting three, Decis plots yielded an average of 1082 g (1,335 kg/ha) while

blue and yellow produced 779 g (962 kg/ha) and 804 g. (993 kg/ha) respectively. There was no

significant difference in yield between plots with blue and yellow traps. There was also no

significant difference in yield between plots with clear traps and the control. Control had the

least mean yield of 460 g. (568 kg/ha).

0

200

400

600

800

1000

1200

1400

1600

1800

Decis Blue Yellow Clear Control

yie

ld o

f Fr

en

ch b

ean

s (

g)

Treatment

a

b b

c c

64


Fig. 4.4 Yield of French beans in planting three

4.5 Discussion

The results obtained in this study showed that colored sticky traps were able to reduce the

number of whiteflies, aphids and thrips on the leaves or flowers of French beans. In all plantings,

the insect populations in plots mounted with blue traps were lower than those recorded in plots

with yellow traps. The results confirm the reported finding by other researchers that blue sticky

traps are more effective on thrips (Muvea, 2011; Covaci et al., 2012; ICIPE, 2011; Harbi et al.,

2013; Elimem et al., 2014). Hoddle et al. (2002) reported that white sticky traps were more

attractive to Frankliniella occidentalis than yellow or blue traps. Other results report that yellow

sticky traps are better in monitoring and controlling of Frankliniella occidentalis (Zepa-Coradini

et et al., 2010). Different hues of colours, possibility of trap materials, reflectance and other

factors next to colour as recorded by the human eye could be playing some part in the effect

which coloured sticky traps exhibit (Kaas, 2005). In this study, rsults have demonstrated that

clear traps had slightly low insect populations compared to control the plots. Currently, thrips

0

200

400

600

800

1000

1200

Decis Yellow Blue Clear Control

yie

ld o

f Fr

en

ch b

ean

s (g

)

Treatment

a

b b

c c

65

rank as primary pests of French beans in Kenya. Frankliniella occidentalis and Megalurothrips

sjostedti being the main thrips species causing 40-60% yield losses at farm level. While M.

sjostedti is said to be manageable using insecticides to uneconomical levels, F. occidentalis has

shown great challenges arising from resistance to most insecticides currently being used by local

farmers (Kasina et al., 2006: Nderitu et al., 2007). Hence blue, yellow and clear traps will be

useful in lowering this species population levels.

This study has also demonstrated that the presence of yellow or blue sticky traps in the field

resulted to the reduction of thrips, aphids and whiteflies. The plots in which these coloured traps

had been mounted produced significantly different higher yields of French beans compared with

the control or clear traps. Coloured sticky traps are usually used to monitor pests either in green

houses or in the field (Lua, et al.,2012; Covaci et al., 2012; Thein et al., 2011; Yaobin et al.;

2012). Most researchers therefore concentrate on the trapped pests on the coloured sticky traps

rather than the impact on population dynamics of the pests. This study indicates that, for the

control of pests, it would also be useful to monitor those pests that are on the plants.

From the results obtained in this study, it is demonstrated that there was a positive effect of blue

and yellow traps in reducing the number of whiteflies (Bemisia tabaci) and Black bean aphid

(Aphis fabae) and that blue traps were slightly better than other traps. Further, it showed that the

coloured traps could be used in the field for whiteflies. Yellow has been reported as the most

attractive colour to alate aphids since it had the highest number of alates caught compared to the

other colours (yellow, blue, green, red, white and black) (Idris, et al., 2012). In a study by

Yaobin, et al., (2012), the impact of yellow sticky traps on the population dynamics of the sweet

potato whitefly, Bemisia tabaci was determined in the greenhouse and field. In contrast to the

66

present study they reported that yellow sticky traps can be used as an effective method for the

control of whiteflies in the greenhouse but not in the field.

In the present study, there was not much difference in aphids, Aphis fabae, present in the plots

with blue or yellow traps. Doring and Chittka (2007), have done a review on behavioral

responses of aphids to stimuli of different colors. They have stated that there is scanty data on

spectral sensitivity to explain aphid behaviour crisply in mechanistic terms. In a report by Straw

et al., (2011) in which a series of field trials were used to assess the practicability of using sticky

traps to monitor populations of green spruce aphid, Elatobium abietinum (Walker), in plantations

of Sitka spruce, significantly more alate aphids were caught on the red sticky traps than on traps

of any other color except for green. Light yellow and green coloured sticky traps have also been

shown to have a significant attractiveness to tea aphid, Toxoptera aurantii (Baoyu et al., 2012).

The yield of French beans for each of the three plantings indicated that both blue and yellow

sticky traps had similar and higher effect on the insects compared to clear and the control.

67

CHAPTER 5

GENERAL DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS

5.1 General discussion

The present study reports an alternative pest management system for French beans. It provides

an easy method of preparation of either Tithonia or Tephrosia extract and spraying to French

beans. Tithonia and Tephrosia emerged as an alternative to chemical pesticides already in use in

crop production. Although the effects of these two extracts were compareable, Tithonia seemed

more specific to thrips. Tagetes and spider plant did not have much insecticidal effect on the

insects. The low effect of Tagetes could be attributed to the method of preparation of the test

materials. If the extract of Tagetes was prepared by distillation of its essential oil or cold organic

extraction, the results may have been different as the insecticidal activity resides in its essential

oil which is volatile (Maradufu, et al. 1978). Tithonia and Tephrosia are either available in the

French bean growing areas or can easily be cultivated by the farmers as hedges or live fences.

The current problem is that our horticultural produce (especially French beans) has raised a red

flag in European countries due to pesticide residues present in the produce. Kenya therefore

needs to relook at biopesticides (Ogola, 2013; Goro, 2013).

Natural insecticides are low in cost, locally available, easy to prepare, safe for the environment

and non target organisms, and insect resistance is not common. The use of plant extracts in

French bean production is a significant contribution to knowledge particularly because small

holder farmers are the major food producers in Kenya and the world over. This study provides

scientific basis for using a more rational approach to integrated pest management in developing

countries where farmers cannot afford high cost of procuring synthetic insecticides. It also

68

provides possible natural alternative techniques that could complement synthetic pesticides.

Blue and yellow sticky traps were also found to be effective alternatives to chemical insecticides

and could be used in integrated the Pest Management programmes.

This study demonstrated that the presence of yellow or blue sticky traps in the field resulted in

the reduction of thrips, aphids and whiteflies. The plots in which these coloured traps had been

mounted produced significantly different higher yields of French beans compared with the

control or clear traps. Coloured sticky traps are usually used to monitor pests either in green

houses or in the field (Covaci et al., 2012; Thein et al., 2011; Yaobin et al.; 2012). Most

researchers therefore concentrate on the trapped pests on the coloured sticky traps rather than the

impact on population dynamics of the pests. This study indicated that, for the control of pests, it

also would be useful to monitor those pests that are on the plants.

5.2 ConclusionsZ

Botanical pesticides at the rate 165 litres of 10% w/v per acre sprayed weekly can be

used to manage pests on French beans and they have the ability to reduce aphid, thrip

and whitefly populations. The most effective extracts were Tephrosia and Tithonia.

Yellow and blue coloured sticky traps were able to reduce insect populations at the

rate of 500 traps per acre.

5.3 Recommendations

Further studies of the conditions and the optimum concentrations, to improve on

quality for use of Tithonia vogelii and Tephrosia diversifolia in French beans should

be studied.

69

Since the blue and yellow colored sticky traps had useful activity on the tested pests,

follow up could be carried out to determine if there would be improved effects if used

together with Tithonia and Tephrosia extracts.

There are no studies of combined extracts of Tithonia and Tephrosia extracts in

French beans and therefore it would be necessary to combine the two and observe the

effects.

The cost of production of French beans when Tithonia and Tephrosia extracts and

coloured traps are used should also be studied.

70

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